Alright, I'm running Windows 7 beta, and it has been bugging me about being a victim of software counterfeiting. Here's what the event viewer says:
Ending session 0 started ‎2009‎-‎09‎-‎27T05:18:49.640625000Z.
Event ID: 10001
... Is Windows 7 punking me?
Edit
Temp update: Been running Champions on max settings for about 30 mins now. GPU is at 55 C, hottest CPU core at 50 C, system is 32 C. Great temps... when/if it reboots this time, I will check the log to see if it says the same weird thing.
Also, I'm getting a "This pre-release version of windows has expired" notification. So I dunno, maybe it's timed shutdowns.