grub-rescue

1. set prefix=(hdX,Y)/boot/grub
Use the values determined earlier. Example: If the Ubuntu system is on sda5, enter: set prefix=(hd0,5)/boot/grub
2.* set root=(hdX,Y)
Example: set root=(hd0,5)
3. insmod normal
Attempt to load the normal module.
4. normal
Activate the normal module. If successful, the GRUB 2 menu may appear.
5. set
(Optional) Review the current settings.
6. ls /boot
(Optional) Check for a vmlinuz and a initrd.img entry.
7. insmod linux
An error message usually means the path is incorrect.
8.* linux /vmlinuz root=/dev/sdXY ro
Selects the latest kernel. Example: linux /vmlinuz root=/dev/sda5 ro
9. initrd /initrd.img
Selects the latest initrd image.
10. boot

http://ubuntuforums.org/showthread.php?t=1854142