there is a nice iso image to download and it's free, called Super Grub Disk
although you can boot into repair mode and then try to fix grub from given menu
other method is to mount ur live ubuntu cd and select Fix Broken System, then mount /dev/sda# (#=-number of ur partition where ubuntu is installed)
drop to root shell and type
If it is the first BIOS drive, this is the same as well:
# grub-install /dev/hd0
if this doesn't work try
# grub-install '(hd0)'
select repair mode, then select from menu UPDATE GRUB CONFIGURATION...
# grub-install /dev/sda