For this (more or less common issue), you might have a try with these:
1) open a shell, login as root
2) nano /boot/grub/menu.lst
3) scroll down and add these lines
And dont forget to change the timeout
value from 0 to something like 5.
4) press ctrl+o , it asks to accept/suggest filename, hit enter
5) hit ctrl+x
6 ) init 6
At reboot you should now find the option Windows selectable.
Hope this helps