If you have lost GRUB due to installation
of Windows while Ubuntu was already installed, you need to follow these steps to
restore it from the live CD
1) Insert live CD and restart system and let the system boot from the live
CD.
2) Now on live Ubuntu, start terminal.
3) Type "sudo grub" and press enter, this will bring the grub prompt.
4) Now at the grub prompt, type "find /boot/grub/stage1" and press enter.
5) Now whatever you get the output from step 4, note it down.
6) Type "root(hd?,?)" and press enter, where you put values returned from step 4 to replace ?.
7) Type "setup(hd?)" and press enter, where replace ? with the value returned from step 4.
8) Type "quit" and press enter to quit grub shell.
9) Restart your system and you will get the GRUB shell waiting for you at the start-up.
2) Now on live Ubuntu, start terminal.
3) Type "sudo grub" and press enter, this will bring the grub prompt.
4) Now at the grub prompt, type "find /boot/grub/stage1" and press enter.
5) Now whatever you get the output from step 4, note it down.
6) Type "root(hd?,?)" and press enter, where you put values returned from step 4 to replace ?.
7) Type "setup(hd?)" and press enter, where replace ? with the value returned from step 4.
8) Type "quit" and press enter to quit grub shell.
9) Restart your system and you will get the GRUB shell waiting for you at the start-up.