Computer total lock-up

Two days ago, my computer started to lock-up when gaming. It only happens on these two games I have been playing: Mafia 2 and Battlefield: Bad Company 2. Source-engine games and GTA IV works fine. (I continue to search more games that crash)

The lock-up is like this: After 15-20min of playing BC2, the picture stops and sound is gone. It doesn't make that shuttering noise, what usually happens when computer freezes.
It doesn't restart. It just stays there. Only thing I can do is press the button.

I've checked temps and they're very good. Logged max 44°C for processor and max 54°C for GPU.


Specs:

Asus M4A78-E with latest BIOS
AMD Phenom II X4 940, @ 3,5Ghz and 1,4V, but reverted back to 3Ghz and 1,35V because of the problem.
Asus Radeon HD 6950 DirectCUII @ 930MHz/1400MHz @ 1,112V, but reverted back to 810Mhz/1250MHz and 1,1V because of the problem.
4GB of DDR2 @ 800MHz RAM. Two sticks of Kingston and two PQI. Same CAS ofc.
Samsung Spinpoint F3 1TB.
Corsair TX650W PSU

Download all latest drivers for your video and sound card. Also make sure to download the latest directx updates with the Directx end-user web installer from the microsoft website.

Let us know how that works out.

Nope. Froze up again.

Any ideas?

EDIT: I googled around and found that other people have problems with 6950 when running BC2.

This topic has been closed by Mousemonkey