If you somehow lost the option to boot into Windows in your GRUB menu, you can get it back by simply adding some text into /boot/grub/menu.lst. Be very careful when editing this file because an error could cause your system to not boot and it would take some work to fix the file.
First, run this command to open up your menu.lst in a text editor:
gksudo gedit /boot/grub/menu.lst
Add the following text to the very end of that file:
title Microsoft Windows
root (hd0,0)
savedefault
makeactive
chainloader +1
Keep in mind that you have to change hd0,0 to whatever is your actual windows partition. Look here to read about the GRUB partition naming scheme and to find out what you should change (hd0,0) to. To get a list of all the partitions on your hard disk you can run this command:
sudo fdisk -l
So, for example, if your windows install was located on /dev/sda3, you would change (hd0,0) to (hd0,2).
October 21, 2007 at 8:04 am
[...] this is the way to add windows back to the boot menu, but only if you have a working installation Restore the Windows boot option to GRUB « Alex S. if your live cd is corrupt and you cant re-install to get the grub boot menu back, then you will [...]
June 24, 2009 at 1:33 am
maybe this could be of some help too http://thetictactoe.wordpress.com/2008/09/24/recover-linux/