Ok, time to get some help instead of giving it ;)
When I play games, my PC randomly reboots (no BSOD). So I tried updating all the drivers, but no succes. I don't have anything overclocked, so that shouldn't be a problem.
My first guess was that something was overheating, so I watched my temps and CPU never is above 50C and GPU never above 60C, which is fine as far as I can tell. I have manually put all fans on higher speeds and that didn't help either.
I think it might be my videocard, as this problem only happens when playing games. Other then that it never crashed and I use it to run some heavy software for my work, like a virtual machine with Linux on it and simultaniously Autocad, firefox, netbeans, etc. This doesn't crash it, but playing a game of Saints Row 3 will.
Windows 7 64 bit
i7 930 @ 2.8 ghz (with somesort of enormous custom cooling thing on it, which the PC-store-guy said "every nerd needed")
6 GB RAM (3x2 triple channel)
Ati Radeon 5700
So any ideas where to start diagnosing?