ArmA freezing after a few minutes

[Archer 0]

So you have tried a 7950 , 8800 , and radion?? video card?

Only thing left might be the memory or motherboard.. again something I had real issues with on my new mobo was drivers not installing correctly because I didn't set the BIOS first to default.

Then had to run through the hardware manager list to make sure everything was snuff.

Sound driver and openAL thingy to recheck, might wanna go back to an older version if you have one you used in the old install.

Video drivers, tried going back to the previous ones you had that used to work?

** I would have suspected the PSU but since it's only messed up since you did a software reinstall, guessing you should start there. You may have the wrong / corrupted drivers for your system. I don't trust driver updates on hardware that hasn't been changed. And someone mentioned a virus; in case you may have forgot to do so, always disconnect the network cable until you install everything OS related including your a/v programs. I know someone that had the same problem and had to do a linux format the drive to get rid of it.  

[Jack-UK 0]

I'm not really sure now, but the instant i read your post i thought it was a PSU problem, i had similar problems before... my PSU did not have sufficient amps on the +12V rail for my system after i upgraded my graphics card to an X1950 PRO.

I upgraded my PSU and my PC worked fine. My PC actually exploded as i kept trying to diagnose the problem. Thankfully only the PSU fried.

If you got any mates with a decent PSU give it a try and see if it works, but you seem to know your stuff by hooking up a PSU to a GFX card lol, so it might not be the PSU if you're sure it isnt.. it was just my initial thoughts.

Hope you get it fixed