its probably a software problem... i had the same thing happen to me several weeks ago...if that automatic restart thing is pissing you off u can turn it off by right clicking on my computer...ahh crap, just realized im in windows ME at the moment... i havent memorized how to turn the automatic restart thing off.... anywho u can't do anything about it... you're probably getting stop errors which means you HAVE to restart...
Its either a program or some driver thats causing windows XP to crash.... PC ALERT III was the program that was causing my comp to crash... i uninstalled it and i haven't had a single stop error since....
has this always been happening?
try to remember what program u installed last... its probably not win XP compatible....