If grub is damaged then system cannot boot at all.

2 wais to fix it:

  • boot live CD with boot-repair program
  • boot live CD and manually reinstall grub

Manual fixing:

  • go to the command prompt (Ubuntu ctrl+alt+F1):
    • sudo su –
    • mkdir /mnt/hdd
    • mount /dev/sda1 /mnt/hdd
    • mount –bind /dev /mnt/hdd/dev/
    • mount –bind /proc /mnt/hdd/proc/
    • mount –bind /sys /mnt/hdd/sys/
    • chroot /mnt/hdd
    • grub-install /dev/sda
    • update-grub