system restore. If you cant do that then try by reinstalling windows xp. You place the disc into the machine restart machine and pressing f12 key and boot form there. At this point try to do a repair, by that way none of your data will be overwritten.
If you can back up your data but by the sounds of what u r saying seems imposssible, but if you can back up data using a pen drive ie transferring all your data files over to your pen drive then reinstalling xp a fresh copy and see if that resolves the problem.
I hpe this can resolve the problem. Also try to get more ram up to 2gb of ram will be sufficient for your desktop or laptop.
If its one of those old celerons they can be pretty slow compared to the new dual celerons it may be worht getting yourself a new computer, if you can.
Any way good luck with your mission.