Överhettning, men var då?

Är på engelska för jag orkar inte skriva allt en gång till. Hoppas ni har överseende med det.

Hey everyone.

After I bought a new graphics card the computer started to shut down when i played games that demanded high graphics performance.

The screen turned black and a sound (like a 5 millisecond sound repeating itself) went on for like 3 seconds and then went off, the fan was still running after that. The computer does not recover itself, I have to restart it manually by holding the on/off button.

I know it's an overheating issue, since the problem goes away when i play without the chassis.

The thing is, the temperatures don't seem to be so high. About 75 C on the graphics card and 53 C on the CPU.
When I run stress-tests on the CPU, GPU and memory, (not simultaneously) nothing happens.
I find this strange since the temp goes higher when i run the tests than when i play games.
Like 85C for the GPU for example.

My guess is that the total accumulated temperature when playing games is higher, and thus is overheating some other part, maybe on the motherboard.
Anyone that knows anything about this? I'll be glad for any help I can get.

Specs:

Graphics: ATI Radeon HD 5750 (the new card)
PSU: 650W Corsair
MB chipset: nForce 720a
memory: 6gig DDR2 RAM

Ska testa att köra Everest, har inte gjort det. Hur funkar det, loggar det värdena så man har dem sen när man rebootar eller?

Har testat att kolla några minuter innan det krashar, på speedfan, men det verkar inte vara något som är konstigt högt där.

Tack för alla svar, nu har jag lite att jobba med!