first, you must know your Windows Administrator account password
apply those steps;
open your PC with Windows XP / Vista CD (bootable)
on blue/white pre installation section, there will be an option available "R to Repair".
Press "R" and wait to Windows CMD open
When CMD opens, it'll ask the Administrator password. If you don't know it, you can't go forward. type these commands;
C:\> Fixboot C:
C:\> Bootcfg /rebuild
then type "EXIT" to restart your PC and Windows will capture boot and open.