• Run Ubuntu Live CD
  • Enter a terminal
  • Locate the linux boot partition lives
    [user@net ~]$sudo fdisk -l
  • Assume the boot partition lives in /dev/sda6 then do mount into a directory, example /mnt/root
  • [user@net ~]$sudo mkdir /mnt/root
  • [user@net ~]$sudo mount -t ext3 /dev/sda6 /mnt/root
  • [user@net ~]$sudo grub-install –root-directory=/mnt/root /dev/sda –recheck
  • reboot

[Source]