It is WIn7. Do you have problems with other games. I have three gameing PC's that I just installed Win7 64 on all of them and now ALL games will shut the PC down. It just dies, no power at all. It would seem alot of people are having this issue on the net, but THREE identical PC at teh same time on the same day, come on, it has to be Win7. Check this thread out http://www.tomshardware.com/forum/3485-63-shutdown-gaming-win7
we are discussing this there.