I have a 3-boot PC with Windows XP, Windows 7 and Ubuntu 12.04, all on different partitions on the same disk. Boot loader is grub for Linux/XP, and Windows XP has an MS boot loader for Windows XP/7. My XP partition had disk problems for some time now, but didn't bother with it, since I didn't use it much. My PC worked without any problems booting or otherwise. After missing for 1 week for business, I came back and found Windows 7 partrition crashed. Had to reformat and reinstall. After reinstall I can boot into Windows 7 fine. However cannot boot into Linux any more
Used the Ubuntu live CD to mount my installation and check the partition table. Using fdisk I toggled the boot flag on the Linux /boot and reboot. I got from the BIOS "Missing Operating System". Verified partition table through fdisk, looks fine. Reconfigured grub, same problem. Even copied all files from /boot to a backup directory, to check for an fs problem (/boot is in its own partition). No problem.
I am now using the Ububtu Live CD, but I cannot keep using it. Each time I loose settings, bookmarks etc. Ran out of ideas. Can you suggest what to try next?