sudo fdisk -l
sudo mkdir -p /media/ubuntu
sudo mount /dev/sda1 /media/ubuntu
Then you need to mount these system folders to use them on your current desktop environment:
sudo mount –bind /dev /media/ubuntu/dev
sudo mount –bind /proc /media/ubuntu/proc
sudo mount –bind /sys /media/ubuntu/sys
Now chroot into your hard drive with this command:
sudo chroot /media/ubuntu
You have now read/write permissions on your root partition. To install GRUB2, you need to use one of these two commands:
# grub-install /dev/sda
Installation finished. No error reported.
Update GRUB2 with this command:
# update-grub
http://askubuntu.com/questions/192332/how-to-repair-grub2-in-a-system-with-broken-recovery-mode