I have 2 Ubuntus installed: 12.04 and 6.10
After I installed the second one - 6.10, the first one (12.04) became invisible in grub.
Then I booted from the 12.04 live cd and followed this http://www.howopensource.com/2012/05/reinstall-recover-grub-from-ubuntu-12-04-live-cd-usb/ article to restore the complete grub using "boot-repair" utility.
Both versions kernels appeared in the list, 12.04 booted fine, but 6.10 became unbootable!
Simply when I chose any of them, the system restarts immediately.
Here is an example of grub entry for this:
Ubuntu, kernel 2.6.17-12-generic (on /dev/sda2)
insmod part_msdos
insmod ext2
set root='(hd0,msdos2)'
search --no-floppy --fs-uuid --set=root f13c4d37-cf48-4e03-91b2-4f4da43a7d73
linux /boot/vmlinuz-2.6.17-12-generic root=/dev/hda2 ro quiet splash
initrd /boot/initrd.img-2.6.17-12-generic
When I change root=/dev/hda2 to root=/dev/sda2 it stops from restarting, but it shows nothing but a command prompt and stops.
I have also tried removing "ro quiet splash" to see any errors with no luck.
I believe this has something to do with sda/hda thing in different Ubuntu versions, but have not had a luck after hours of searching to determine the solution!
Here is the output of "boot info script":
http://pastebin.com/raw.php?i=pVMdHkax
(Couldn't figure out how to correctly attach it here).
Thanks for looking.