Jump the CMOS for ~1 minute. Put the jumper back and then remove the battery for another ~1 minute. Put it back in and start up the computer and immediately go into the BIOS and set the boot order as 1. CD-ROMS 2. Floppy (if you have one) 3. Hard Disk Drives. Open the drive and put in your Windows XP CD, save the changes and let it restart. Once it restarts boot from the CD and delete your partition on your main drive (C) This will remove EVERYTHING from the drive so if you want any data backed up you will have to boot into safe mode first and burn a CD or stick it on another drive. After you delete the partition recreate it (usually c) and then do a full format (not quick format) of that partition. After it's done re-install Windows XP and THEN re-install all your drivers, usually in order of System, graphical, sound, then all the other stuff you may need for any PCI cards or USB ports. After all that is said and done and you're STILL having problems with your machine post back with an update.