if its winxp, u put the cd in, boot up the comp, it will take u to the win xp install screen, gives u 3 ops, one of em i think is repair, i go to that option, then it takes u to dos asking which installation of windows to repair, type in 1 and enter, then type C:\format, and it will format the drive, or there may be a option in the instalation menu that says to format, i cant remember