I've seen this due to driver issues as well as virus infections. Given that it never worked (you didn't reveal much) I just try installing the motherboard chipset drivers in safe mode or start over.
When I start up the computer I am able to use the mouse and keboard to enter Bios, however once windows xp loads the usb ports are disabled. The major issue is that i have no sp2 ports so I have no alternative for my mouse and keyboard. I am unable to do anything outside of BIOS. I tried restoring and entering in Safe Mode but I'm still not getting anywhere. Please Help!