is your computer a compaq? or is your windows xp, (god forbid), copied from a friend, or not bought from a store.
if it is a compaq, most compaqs will not support windows xp, and will just shut the operating system down. i have found this out through personal experince and hours on the phone with compaq. i now only use this gateway im typing to you on i got so fed up with compaq :-d.
if its a copy or illegal, then windows xp really has started cracking down on illegal software. they will shutdown the OS remotly if they detect (and theirs about a 85%-90% chance they will). Also i've heard rumors that sometimes when this happens other parts of your computer may go/brake too when this happens. Don't know why but it happend to two of my friends.