Ubuntu install with rEFIt on MacBook pro: Grub apparently messed up my Windows 7 boot

[Kaitain]

This seems to be a variant of a problem many people have had, but after several hours trawling through various forums, I haven't seen a reliable match for my situation.

In brief:
Adding a third boot partition (of Ubuntu) to my existing dual boot of OSX 10.6 and Windows 7 seems to have crippled the Windows boot from working, because Grub apparently takes over the process. Yet Grub does *not* appear to be on the Windows partition.

More verbose:
I have an older MacBook Pro (3.1, running Snow Leopard) that I recently refitted with a new 240GB SSD HD. With the extra space (it was previously only 120GB) I decided to add a dual boot with Windows 7 using bootcamp. This all went swimmingly well. Encouraged, I decided to follow this Lifehacker article's suggestion and triple-boot the machine with Ubuntu (I'd never used Linux before):

http://lifehacker.com/#!5531037/how-...-camp-required

So I now have the nice rEFIt boot partition selection screen, and, indeed, I'm up and running in Ubuntu, and enjoying it.

Only one problem: I can't get into Windows any more. If I try to go in through rEFIt *or* by holding down OPT at startup and selecting the windows partition directly, the result is the same: I get thrown into Grub's selector, and selecting the Windows partition from there leads to an error message and a dead end.

Having read through numerous postings, I get the impression that Grub is doing something or living somewhere that it ought not to be, but in most cases I've seen, people had accidentally installed Grub onto the Windows partition (or indeed onto EVERY partition). So far as I can tell, this isn't the case with me. Here's my boot summary:

Boot Info Script 0.55    dated February 15th, 2010                    

============================= Boot Info Summary: ==============================

 => Grub 2 is installed in the MBR of /dev/sda and looks at sector 283485000 
    of the same hard drive for core.img, but core.img can not be found at this 
    location.

sda1: _________________________________________________________________________

    File system:       vfat
    Boot sector type:  BSD4.4: Fat32
    Boot sector info:  According to the info in the boot sector, sda1 starts 
                       at sector 0. But according to the info from fdisk, 
                       sda1 starts at sector 40.
    Operating System:  
    Boot files/dirs:   

sda2: _________________________________________________________________________

    File system:       hfsplus
    Boot sector type:  -
    Boot sector info:  
    Operating System:  
    Boot files/dirs:   

sda3: _________________________________________________________________________

    File system:       ext4
    Boot sector type:  -
    Boot sector info:  
    Operating System:  Ubuntu 10.10
    Boot files/dirs:   /boot/grub/grub.cfg /etc/fstab /boot/grub/core.img

sda4: _________________________________________________________________________

    File system:       swap
    Boot sector type:  -
    Boot sector info:  

sda5: _________________________________________________________________________

    File system:       vfat
    Boot sector type:  BSD4.4: Fat32
    Boot sector info:  According to the info in the boot sector, sda5 starts 
                       at sector 0. But according to the info from fdisk, 
                       sda5 starts at sector 314015744.
    Operating System:  
    Boot files/dirs:   

sda6: _________________________________________________________________________

    File system:       ntfs
    Boot sector type:  Windows Vista/7
    Boot sector info:  No errors found in the Boot Parameter Block.
    Operating System:  Windows 7
    Boot files/dirs:   /bootmgr /Boot/BCD /Windows/System32/winload.exe

=========================== Drive/Partition Info: =============================

Drive: sda ___________________ _____________________________________________________

Disk /dev/sda: 240.1 GB, 240057409536 bytes
255 heads, 63 sectors/track, 29185 cylinders, total 468862128 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes

Partition  Boot         Start           End          Size  Id System

/dev/sda1                   1       409,639       409,639  ee GPT
/dev/sda2    *        409,640   273,847,143   273,437,504  af HFS
/dev/sda3         274,110,464   310,370,303    36,259,840  83 Linux
/dev/sda4         310,370,304   314,015,743     3,645,440  82 Linux swap / Solaris


GUID Partition Table detected.

Partition           Start           End          Size System
/dev/sda1              40       409,639       409,600 System/Boot Partition
/dev/sda2         409,640   273,847,143   273,437,504 HFS+
/dev/sda3     274,110,464   310,370,303    36,259,840 Linux or Data
/dev/sda4     310,370,304   314,015,743     3,645,440 Linux Swap
/dev/sda5     314,015,744   332,816,383    18,800,640 Linux or Data
/dev/sda6     332,816,384   468,860,927   136,044,544 Linux or Data

blkid -c /dev/null: ____________________________________________________________

Device           UUID                                   TYPE       LABEL                         

/dev/sda1        70D6-1701                              vfat       EFI                           
/dev/sda2        c5bee107-051f-385e-8555-0eabcd9552b1   hfsplus    Macintosh HD                  
/dev/sda3        4e6b4af7-35b2-46a0-bd0f-6a385e7c18a3   ext4                                     
/dev/sda4        17c1e3bb-f9de-4584-b43a-a8022f79b8b4   swap                                     
/dev/sda5        71C8-1202                              vfat       SHARED                        
/dev/sda6        CE7A834E7A83326F                       ntfs       BOOTCAMP                      
/dev/sda: PTTYPE="gpt" 

============================ "mount | grep ^/dev  output: ===========================

Device           Mount_Point              Type       Options

/dev/sda3        /                        ext4       (rw,errors=remount-ro,user_xattr,commit=600)


=========================== sda3/boot/grub/grub.cfg: ===========================

#
# DO NOT EDIT THIS FILE
#
# It is automatically generated by grub-mkconfig using templates
# from /etc/grub.d and settings from /etc/default/grub
#

### BEGIN /etc/grub.d/00_header ###
if [ -s $prefix/grubenv ]; then
  set have_grubenv=true
  load_env
fi
set default="0"
if [ "${prev_saved_entry}" ]; then
  set saved_entry="${prev_saved_entry}"
  save_env saved_entry
  set prev_saved_entry=
  save_env prev_saved_entry
  set boot_once=true
fi

function savedefault {
  if [ -z "${boot_once}" ]; then
    saved_entry="${chosen}"
    save_env saved_entry
  fi
}

function recordfail {
  set recordfail=1
  if [ -n "${have_grubenv}" ]; then if [ -z "${boot_once}" ]; then save_env recordfail; fi; fi
}

function load_video {
  insmod vbe
  insmod vga
}

insmod part_gpt
insmod ext2
set root='(hd0,gpt3)'
search --no-floppy --fs-uuid --set 4e6b4af7-35b2-46a0-bd0f-6a385e7c18a3
if loadfont /usr/share/grub/unicode.pf2 ; then
  set gfxmode=640x480
  load_video
  insmod gfxterm
fi
terminal_output gfxterm
insmod part_gpt
insmod ext2
set root='(hd0,gpt3)'
search --no-floppy --fs-uuid --set 4e6b4af7-35b2-46a0-bd0f-6a385e7c18a3
set locale_dir=($root)/boot/grub/locale
set lang=en
insmod gettext
if [ "${recordfail}" = 1 ]; then
  set timeout=-1
else
  set timeout=10
fi
### END /etc/grub.d/00_header ###

### BEGIN /etc/grub.d/05_debian_theme ###
set menu_color_normal=white/black
set menu_color_highlight=black/light-gray
### END /etc/grub.d/05_debian_theme ###

### BEGIN /etc/grub.d/10_linux ###
menuentry 'Ubuntu, with Linux 2.6.35-27-generic' --class ubuntu --class gnu-linux --class gnu --class os {
	recordfail
	insmod part_gpt
	insmod ext2
	set root='(hd0,gpt3)'
	search --no-floppy --fs-uuid --set 4e6b4af7-35b2-46a0-bd0f-6a385e7c18a3
	linux	/boot/vmlinuz-2.6.35-27-generic root=UUID=4e6b4af7-35b2-46a0-bd0f-6a385e7c18a3 ro   quiet splash
	initrd	/boot/initrd.img-2.6.35-27-generic
}
menuentry 'Ubuntu, with Linux 2.6.35-27-generic (recovery mode)' --class ubuntu --class gnu-linux --class gnu --class os {
	recordfail
	insmod part_gpt
	insmod ext2
	set root='(hd0,gpt3)'
	search --no-floppy --fs-uuid --set 4e6b4af7-35b2-46a0-bd0f-6a385e7c18a3
	echo	'Loading Linux 2.6.35-27-generic ...'
	linux	/boot/vmlinuz-2.6.35-27-generic root=UUID=4e6b4af7-35b2-46a0-bd0f-6a385e7c18a3 ro single 
	echo	'Loading initial ramdisk ...'
	initrd	/boot/initrd.img-2.6.35-27-generic
}
menuentry 'Ubuntu, with Linux 2.6.35-22-generic' --class ubuntu --class gnu-linux --class gnu --class os {
	recordfail
	insmod part_gpt
	insmod ext2
	set root='(hd0,gpt3)'
	search --no-floppy --fs-uuid --set 4e6b4af7-35b2-46a0-bd0f-6a385e7c18a3
	linux	/boot/vmlinuz-2.6.35-22-generic root=UUID=4e6b4af7-35b2-46a0-bd0f-6a385e7c18a3 ro   quiet splash
	initrd	/boot/initrd.img-2.6.35-22-generic
}
menuentry 'Ubuntu, with Linux 2.6.35-22-generic (recovery mode)' --class ubuntu --class gnu-linux --class gnu --class os {
	recordfail
	insmod part_gpt
	insmod ext2
	set root='(hd0,gpt3)'
	search --no-floppy --fs-uuid --set 4e6b4af7-35b2-46a0-bd0f-6a385e7c18a3
	echo	'Loading Linux 2.6.35-22-generic ...'
	linux	/boot/vmlinuz-2.6.35-22-generic root=UUID=4e6b4af7-35b2-46a0-bd0f-6a385e7c18a3 ro single 
	echo	'Loading initial ramdisk ...'
	initrd	/boot/initrd.img-2.6.35-22-generic
}
### END /etc/grub.d/10_linux ###

### BEGIN /etc/grub.d/20_linux_xen ###
### END /etc/grub.d/20_linux_xen ###

### BEGIN /etc/grub.d/20_memtest86+ ###
menuentry "Memory test (memtest86+)" {
	insmod part_gpt
	insmod ext2
	set root='(hd0,gpt3)'
	search --no-floppy --fs-uuid --set 4e6b4af7-35b2-46a0-bd0f-6a385e7c18a3
	linux16	/boot/memtest86+.bin
}
menuentry "Memory test (memtest86+, serial console 115200)" {
	insmod part_gpt
	insmod ext2
	set root='(hd0,gpt3)'
	search --no-floppy --fs-uuid --set 4e6b4af7-35b2-46a0-bd0f-6a385e7c18a3
	linux16	/boot/memtest86+.bin console=ttyS0,115200n8
}
### END /etc/grub.d/20_memtest86+ ###

### BEGIN /etc/grub.d/30_os-prober ###
menuentry "Mac OS X (32-bit) (on /dev/sda2)" {
	insmod part_gpt
	insmod hfsplus
	set root='(hd0,gpt2)'
	search --no-floppy --fs-uuid --set e57c5db0b8b4f67f
        load_video
        set do_resume=0
        if [ /var/vm/sleepimage -nt10 / ]; then
           if xnu_resume /var/vm/sleepimage; then
             set do_resume=1
           fi
        fi
        if [ $do_resume = 0 ]; then
           xnu_uuid e57c5db0b8b4f67f uuid
           if [ -f /Extra/DSDT.aml ]; then
              acpi -e /Extra/DSDT.aml
           fi
           xnu_kernel /mach_kernel boot-uuid=${uuid} rd=*uuid
           if [ /System/Library/Extensions.mkext -nt /System/Library/Extensions ]; then
              xnu_mkext /System/Library/Extensions.mkext
           else
              xnu_kextdir /System/Library/Extensions
           fi
           if [ -f /Extra/Extensions.mkext ]; then
              xnu_mkext /Extra/Extensions.mkext
           fi
           if [ -d /Extra/Extensions ]; then
              xnu_kextdir /Extra/Extensions
           fi
           if [ -f /Extra/devprop.bin ]; then
              xnu_devprop_load /Extra/devprop.bin
           fi
           if [ -f /Extra/splash.jpg ]; then
              insmod jpeg
              xnu_splash /Extra/splash.jpg
           fi
           if [ -f /Extra/splash.png ]; then
              insmod png
              xnu_splash /Extra/splash.png
           fi
           if [ -f /Extra/splash.tga ]; then
              insmod tga
              xnu_splash /Extra/splash.tga
           fi
        fi
}
menuentry "Mac OS X (64-bit) (on /dev/sda2)" {
	insmod part_gpt
	insmod hfsplus
	set root='(hd0,gpt2)'
	search --no-floppy --fs-uuid --set e57c5db0b8b4f67f
        load_video
        set do_resume=0
        if [ /var/vm/sleepimage -nt10 / ]; then
           if xnu_resume /var/vm/sleepimage; then
             set do_resume=1
           fi
        fi
        if [ $do_resume = 0 ]; then
           xnu_uuid e57c5db0b8b4f67f uuid
           if [ -f /Extra/DSDT.aml ]; then
              acpi -e /Extra/DSDT.aml
           fi
           xnu_kernel64 /mach_kernel boot-uuid=${uuid} rd=*uuid
           if [ /System/Library/Extensions.mkext -nt /System/Library/Extensions ]; then
              xnu_mkext /System/Library/Extensions.mkext
           else
              xnu_kextdir /System/Library/Extensions
           fi
           if [ -f /Extra/Extensions.mkext ]; then
              xnu_mkext /Extra/Extensions.mkext
           fi
           if [ -d /Extra/Extensions ]; then
              xnu_kextdir /Extra/Extensions
           fi
           if [ -f /Extra/devprop.bin ]; then
              xnu_devprop_load /Extra/devprop.bin
           fi
           if [ -f /Extra/splash.jpg ]; then
              insmod jpeg
              xnu_splash /Extra/splash.jpg
           fi
           if [ -f /Extra/splash.png ]; then
              insmod png
              xnu_splash /Extra/splash.png
           fi
           if [ -f /Extra/splash.tga ]; then
              insmod tga
              xnu_splash /Extra/splash.tga
           fi
        fi
}
menuentry "Windows 7 (loader) (on /dev/sda6)" {
	insmod part_gpt
	insmod ntfs
	set root='(hd0,gpt6)'
	search --no-floppy --fs-uuid --set ce7a834e7a83326f
	chainloader +1
}
### END /etc/grub.d/30_os-prober ###

### BEGIN /etc/grub.d/40_custom ###
# This file provides an easy way to add custom menu entries.  Simply type the
# menu entries you want to add after this comment.  Be careful not to change
# the 'exec tail' line above.
### END /etc/grub.d/40_custom ###

### BEGIN /etc/grub.d/41_custom ###
if [ -f  $prefix/custom.cfg ]; then
  source $prefix/custom.cfg;
fi
### END /etc/grub.d/41_custom ###

=============================== sda3/etc/fstab: ===============================

# /etc/fstab: static file system information.
#
# Use 'blkid -o value -s UUID' to print the universally unique identifier
# for a device; this may be used with UUID= as a more robust way to name
# devices that works even if disks are added and removed. See fstab(5).
#
# <file system> <mount point>   <type>  <options>       <dump>  <pass>
proc            /proc           proc    nodev,noexec,nosuid 0       0
# Commented out by Dropbox
# /dev/sda3       /               ext4    errors=remount-ro 0       1
/dev/sda4       none            swap    sw              0       0
/dev/sda3 / ext4 errors=remount-ro,user_xattr 0 1

=================== sda3: Location of files loaded by Grub: ===================


 145.1GB: boot/grub/core.img
 155.6GB: boot/grub/grub.cfg
 142.3GB: boot/initrd.img-2.6.35-22-generic
 143.0GB: boot/initrd.img-2.6.35-27-generic
 145.1GB: boot/vmlinuz-2.6.35-22-generic
 145.1GB: boot/vmlinuz-2.6.35-27-generic
 143.0GB: initrd.img
 142.3GB: initrd.img.old
 145.1GB: vmlinuz
 145.1GB: vmlinuz.old

I was considering trying to execute a repair with my Windows 7 CD tonight, but it doesn't seem obvious to me that this would help, given that Grub isn't actually living in that partition.

I've also wondered whether there might be a problem having Windows 7 on a later partition rather than sitting adjacent to the OSX partition. (I resized the OSX downwards so that I could create the small partition for Ubuntu, which sits in the middle and appears as the second option in the rEFIt selection screen.)

Not sure if the boot summary's mention of the core.img file not being located where the system was expecting is of relevance.

Any suggestions gratefully received.

K

[srs5694]

Your problem is that your Windows partition no longer appears in your hybrid MBR. Presumably it's been "bumped out" by your Linux partition(s) when you repartitioned for Linux.

Fortunately, the fix is fairly easy (although detail-oriented), but I recommend you read the hybrid MBR page to which I just linked before proceeding:

1. Download my GPT fdisk (gdisk) from its Sourceforge download page. (Do not install the version in the Ubuntu repositories; that version is ancient and has known bugs.) You can download either the OS X or the Linux version (a .deb file for your architecture, either i386 or amd64); either will work.
2. Install the GPT fdisk package that you downloaded. Double-clicking should do the job in either OS X or Linux.
3. Open a Terminal window.
4. Type "sudo gdisk /dev/sda" (in Ubuntu) or "sudo gdisk /dev/disk0" (in OS X). This will launch gdisk
5. Type "p" to view your partition table, just as a sanity check. It should show the same partitions that GParted or other utilities show. (Note that OS X's Disk Utility omits the EFI System Partition, though.) If your table looks wrong, exit by typing "q" and investigate further before proceeding.
6. Type "r" to enter the recovery & transformation menu. The gdisk prompt will change.
7. Type "h" to create a new hybrid MBR. You'll be prompted to type up to three partition numbers. It looks like you'll want to type either "5 6" or "6 5" -- your Windows and shared-data partitions. You'll be prompted for more information. Tell it to put the 0xEE partition first in the table. Change the type code of the FAT partition to 0c and answer "Y" to the prompt about setting the Windows partition's boot/active flag. There's no point in creating a second protective partition in your case, so tell it not to do so.
8. When it's done and you get back to the main gdisk prompt, type "o" to view the MBR partition table. It should include the Windows and shared-data partitions (identifiable by their start and end sectors; compare to the "p" output) and a partition of type 0xEE that covers most of the rest of the disk. If this looks wrong, either type "h" to try again or type "q" to quit, research it more, and try again when you better understand it.
9. Type "w" to save your changes.

There's a good chance that Windows will boot from the rEFIt menu at this point, but I can't guarantee that. If it doesn't, see if there's a Windows option in the GRUB menu and, if there is, try to boot using that. Post back with details about what's going wrong. It's possible that adjusting the partitions you include in the hybrid MBR will help Windows boot (Windows is very finicky about its boot partition!); or you might need to use the Windows recovery CD/DVD to restore Windows to bootability.

[Kaitain]

Most grateful for the speedy (and detailed) reply.

Will try that tonight and let you know how it goes.

Out of interest, would things have gone any more smoothly had I put Windows on after Linux rather than vice versa?

K.

[srs5694]

Out of interest, would things have gone any more smoothly had I put Windows on after Linux rather than vice versa?

Probably not, and that would present another pitfall of Windows (perhaps) wiping out the part of GRUB that's installed to the MBR (if in fact that's where you put it). The issue here is that a hybrid MBR can hold only three real partitions, and most tools that create hybrid MBRs just blindly grab the first three partitions they come across for inclusion in the hybrid MBR, without any concern for whether the OSes that actually use those partitions need the partitions to be there. Both OS X and Linux understand GPT, and so don't need their partitions in the hybrid MBR; but because you put the OS X and Linux partitions earlier on the disk than the Windows partitions, it was the OS X and Linux partitions that got included in your hybrid MBR, leaving the Windows partitions (which do need to be there) out in the cold.

FWIW, when you're done, this layout will actually be superior to what you'd have if you'd put the Windows partitions first on the disk. The reason is that your hybrid MBR will contain a protective (type-0xEE) partition that will cover the OS X and Linux partitions. If Windows were first on the disk, the usual hybrid MBR tools would create a hybrid MBR that would include Windows, but you'd then have a big part of the disk that would seem (from Windows) to be unpartitioned, when in fact it would hold Linux and OS X. That opens up the possibility for a disk utility to create "new" MBR partitions in the "unpartitioned" space, thus trashing Linux and/or OS X. With your current layout, that won't be possible -- at least, not without first deleting the 0xEE partition.

[Kaitain]

This is all very informative stuff. Thanks.

To further my understanding of what's happening, are you able to tell me why the Mac's built-in drive selector (holding down opt on restart) displays the Windows partition as an option (one of two, with rEFIt being the others) but is not actually boot to it if selected? Is the MBR misdirecting it when the selection is made?

Also, why does Windows fail to load even when selected as an option from the Grub menu? Is Grub expecting only to be launching a version of Linux?

One other thing: if I wiped out all the Ubuntu and Windows partitions, and then reinstalled Windows 7 from scratch as a second partition, should I expect to have Windows back in working order, or would the MBR still need to be tinkered with?

Thanks again.

[srs5694]

To further my understanding of what's happening, are you able to tell me why the Mac's built-in drive selector (holding down opt on restart) displays the Windows partition as an option (one of two, with rEFIt being the others) but is not actually boot to it if selected? Is the MBR misdirecting it when the selection is made?

I don't know enough about the Mac's built-in boot selector to answer this authoritatively. My guess, however, is that it's scanning the GPT partitions, finding a Windows installation, and offering to boot it without checking that it's got a valid MBR entry (which it doesn't have). Windows then fails to boot (see below).

Also, why does Windows fail to load even when selected as an option from the Grub menu? Is Grub expecting only to be launching a version of Linux?

This is a Windows problem, not a GRUB problem. Microsoft refuses to enable their OS to boot on GPT disks on BIOS-based computers, or to support the version of EFI that Apple uses. To boot Windows at all on Macs, Apple has chosen to use a BIOS emulation layer in its EFI. Thus, Macs look like BIOS-based computers to Windows.

This interacts with Microsoft's interpretation of hybrid MBR disks. Unlike Linux and OS X, which give the GPT side precedence, when Windows sees a hybrid MBR disk, it gives the MBR side precedence. Thus, Windows doesn't even know that partitions other than the ones it sees in the MBR exist on the disk. Windows therefore can't boot, since it can't see its own boot partition.

As you may be gathering by now, the ability of Windows to boot on Macs is a rickety house of cards. Remove one card and the whole thing collapses. It's an ugly, ugly hack.

One other thing: if I wiped out all the Ubuntu and Windows partitions, and then reinstalled Windows 7 from scratch as a second partition, should I expect to have Windows back in working order, or would the MBR still need to be tinkered with?

It depends on how you did it, and I can't even give you detailed instructions on how to do it in a way that would work. IMHO, you're better off following the instructions I gave earlier.

[Kaitain]

Okay. Am typing this from Opera running on Windows.

At first I thought it hadn't worked, because it still threw me into Grub. But now selecting the Windows partition from the list of options in Grub launches Windows successfully. Not QUITE as nice as going there straight from the natty rEFIt menu, but that's like complaining about scratched paintwork when your car's just been repaired for free.

You, sir, are a gentleman and a scholar. I am very grateful.

btw I am assuming (?) that the Windows partition's hex code was to be left at the default value, and only the shared FAT partition's code changed to 0c?

K

[srs5694]

btw I am assuming (?) that the Windows partition's hex code was to be left at the default value, and only the shared FAT partition's code changed to 0c?

I'm glad it's (mostly) working now. Yes, you should only have changed the FAT partition's type code. The value for the NTFS partition should have been 0x07, which is correct.

As to rEFIt, I'm not sure why it's not working at this point. Perhaps you can dig into the rEFIt configuration files to find some tweak to get it working. I'm afraid that my knowledge of rEFIt is a bit limited, so I can't offer any more specific suggestions.

[Kaitain]

To clarify, the rEFIt menu still appears, and selecting the Apple icon takes me straight through to OSX. But selecting either the Linux or the Windows icon will take me through to Grub, from where I need to make the actual OS selection, i.e. to all intents and purposes the Linux and Windows options jointly constitute a single "Grub" button, and the real choice has to be made via Grub.

I could try reinstalling rEFIt, but at this point I'm not sure I want to tempt fate just for the sake of aesthetics.

[srs5694]

Ah, I see. It sounds to me like GRUB got installed to the MBR, overwriting the Windows boot loader. Presumably rEFIt is just probing the MBR, and not the Windows boot partition, for boot code, so when it finds code in the MBR, it thinks it's Windows code and gives you a menu option for Windows that launches GRUB. This is speculative, but it fits the facts.

You could probably get it working by re-installing GRUB to the Linux root (/) or (if you've got one) /boot partition and then using Windows utilities to re-install the Windows boot loader to the MBR. There is a risk that by trying this you'd end up damaging the ability to boot one or more OSes, though. Only you can decide if it's worth the risk of trying.