There a number of things that could be causing your problem. completely disconnect your keyboard and mouse and reboot system, shut down completly, plug keyboard and mouse back in and start the computer, you should get a message that new devices have been found and windows will attempt to locate the device drivers for them. If sucessfull, your keyboard and mouse should be back on. If not try a different keyboard and see what happens. If still nothing then I would suspect a problem with your Win XP, try reinstalling over the existing O/S and restart, if that does not work, I would suspect a mobo malfunction and replace mobo or build new computer using whatever existing parts you can get out of the old computer.