> Yes, I verified that the Ubuntu Boot Partition is still selected as the
> partition to boot the Ubuntu menu item. Boot edit is still configured
> correctly, as it was before the problem occurred. And all the Ubuntu
> partitions are mapped to the Ubuntu menu entry. All of that should have
> been restored when I restored the BootIt partition from the backup image,
> and as far as I can tell, everything is still configured the same as it was
> when it was working correctly.
> The MBR partition is the FAT16 partition at the beginning of the HDD,
> covering LBA's 63 through 80324. It was created as part of the original
> Windows installation (when I bought my PC - before I added any additional
> I can't help thinking that whatever changed must be somewhere other than in
> the partitions I restored from backup (which includes all the Ubuntu
> partitions, plus the BootIt partition). But I can't imagine what else it
> could be - all the other OS's are booting and working correctly. I'm
> really at a loss here. What are the other possibilities?
The most common problem with something like this is that the grub2 boot loader is damaged, and needs to be reinstalled.
The KB article linked below has a procedure that you can work through step by step to see if you can boot into Ubuntu manually from a Grub2 boot disk (link provided in the article), and then reinstall Grub2 from the command line within Ubuntu. Be sure not to skip step 2, which is to attempt booting Ubuntu from the BIBM menu before booting from the grub2 boot disk, even though you know it will fail. That is done to ensure that the Ubuntu partitions are loaded into the MBR, so that they can be accessed from the Grub2 boot disk.http://www.terabyteunlimited.com/kb/article.php?id=408
Note that if the attempt to boot into Ubuntu in step 5 fails, see "Issue 2" in the troublshooting section at the end of the article for an alternate method of manually booting into Ubuntu.