arial -
Welcome to TechIMO

!.
To me, it sounds as if you are having a hardware / temp problem.
First thing I would check to verify this is to see if you can get in the BIOS (tap the delete key while it's booting). If you can, check you're temps (if you can).
Did you build this system? What are you using as a heatsink?
If you can get into the BIOS and the temps look OK (30º to 42º C), you may want to try booting with just the basics (1 stick of good memory, video card, floppy, and hard drive).
If still you can't get it to boot, I would start thinking maybe a virus

. That's out in left field though - the only time I've seen XP get
really flaky and quit is from either a bad driver (immediatly) or temps (overclocking too much).
Let us know what happens.
Mike