Having major GPU component issues.

Greetings all,

I have two fairly old computers, of which I cannot remember the specs exactly
1. Family Computer
CPU: Athlon 3800+
Motherboard: Elitegroup K8T something (has both AGP and PCI-E slots)
RAM: 2gb DDR 400 speed
GPU: 7600GT (currently)
PSU: RAIDMAX 730 watt modular

2. Game Computer
CPU: Athlon 4400+
Motherboard: nForce 570 Ultra
RAM: 2gb corsair 800 speed
GPU: Radeon 4650 (currently)
PSU: RAIDMAX 530 watt modular

My issue is that the videocards I put into these machines seemly break and suffer (what I think is) major heating/cooling problems.

The computers have the same issues and they are:
1. The videocards start to pixilate and crash whenever doing something graphical such as games or even HD videos - then a VPU recovery prompt occurs.
2. Using the CCC to put the cards at their lowest core and memory speed as well as pushing the fan to max speed does seem to let the cards function, at least for a little bit while playing games.
3. ATItool seemly suggests that my 4850 (the only card I tested it on) says the core speed is at negative 2 million.

My 4870 from my main computer worked fine in these machines to the best that I could see of, but no videocards from these two broken computers worked in my main computer (at least not for long). So far the cards that i have tested and seemly lost are a 4850, 4650, 7600GT, and 1900XT.

What could possibly be the issue? It seemly spread from the Family Computer to the Game Computer, the only real commonality between the two is that they used the same videocards. Formatting and intense virus scanning (with avast) did nothing to absolve the issue.