If the cover is off with a cooling fan pointed at the case does that help?
It's a test to see if it's heat related.
i previously posted here about the same problem () and i took his advise by cleaning the inside of my computer. It worked for a while and then it started re starting again. But sometimes I was actually able to stAY logged in for about 10 min before it freezes. This used to never happen on this computer. Someone told me if i installed new hardware that might have been the problem but i didnt get anymore info about that (i just got a dvd-rw drive from pioneer) any help is appreciated thanks!