I have a windows xp professional computer which is a couple years old. The computer starts up, everything seems fine and right beofre the login screen loads it shuts down. It used to just restart the computer over and over again but now it just turns off completely. This happened once a couple months ago but it started working after a couple days, and everything was working fine. I don't want to lose all my files and I want it to work again! any tips!? help!