Use this when your MBR gets corrupted – usually happens after you reinstall windows. Pop in a bootable ubuntu DVD and boot into it. Then open a terminal and type in the following commands…
$ sudo grub
> find /boot/grub/stage1
(hd0,1)
> root (hd0,1) #Must be same as the output of the last command
> setup (hd0)
$ sudo grub
> find /boot/grub/stage1
(hd0,1)
> root (hd0,1) #Must be same as the output of the last command
> setup (hd0)