My guess, reinstallin windows :shock:
"The BIOS can be accessed when you start your computer. You may see a reference to "setup" when you turn your computer on. That's your opportunity to get into the BIOS. It usually requires the push of a function key, such as F10, to get access to it. That "F" key varies between computers. Sometimes it's the ESC key or DEL key."
Then go to the Boot sreen and change the the drive from wich your computer boots...
It should be set to your primary hardrive, so just set it to your CD or DVD drive.
Put your XP cd in the drive , reboot and voila.