|If you get the option 'Last known good configuration' then choose that.|
Use XP install disk or recovery disk to do a start up repair.
IF these do not work then test your memory with Memtest86
AND test your hard drive with the hard drive manufacturer's hard drive utility that you can download from their website (Yes you will need to remove one of those covers on the bottom that is held closed by a screw in order to see what brand the hard drive is).
You have to be a little bit crazy to keep you from going insane.