Is the error which you get while accessing windows something like this
cannot locate WINDOWS/SYSTEM32/winload.exe
ERROR CODE something something
If your problem is similar to above then you need to do the following task
Boot into your linux
$ fdisk -l
which will show your disk partitons from which you identify your windows drive device say it is sda2
Become root and open /boot/grub/menu.lst into a text editor and locate the windows entry there .
What you need to do here to edit the entry something like
title windows 1
rootnoverify (hd0,5) // it may be different in your case.
chainloader (hd0,0)+1
and rectify the entry to the proper one which in case of the windows drive being sda2 will be (hd0,1)
It goes something like this
sdaX implies hd(X-1)
Your winload.exe should be back now.