1) Boot from a Live CD
2) Open a terminal window or switch to a TTY and enter:
sudo grub
3) At the grub prompt, use the following command to determine where grub is installed:find /boot/grub/stage1
4) Using the hard disk and partition given by the above, enter:root (hd0,6)
setup (hd0)
5) Then quit grub by typing quit, and reboot your machine.If you need more information about the partitions on your disk, use:
sudo fdisk -l
Note that the partition numbers shown by fdisk begin at zero; grub however uses a zero-based index, so you'll need to subtract one from the number given by fdisk.