Computer reboots after about 2-5 mins, OR hangs on high 3D graphics games

The card works fine whit no driver, but hangs or reboot after a few min. with latest drivers from ATI (maybe they return to theyr habit of making bad drivers :( again). PS: heat problem is out of the question (3 minutes in 12C enviroment temp with open case). DXdiag crashes on Direct3D test. Some game and all aplications works fine for hours, so I don't think is a heat problem

Sounds like an overheating problem. The increased demands on the video card create a lot of heat that is most likely not being dissipated properly. Two suggestions - does the graphics card have a dedicated fan? I am assuming it does, and it likely runs at one speed all of the time. Ensure that the fan is actually spinning when the computer is powered up. Another possibility is to add a whole case fan to push heat out of the computer case (most computers do not come with them but usually have the vent and mounting holes in the back to install one, and a connector on the Motherboard to plug it in - I added one to one of mine that was overheating and it is easy and relatively cheap). Also make sure the computer has free flow of fresh air around it. I have seen many cases where the computer case was put in a computer desk where the case is closed up behind a swinging door with one little vent hole. These do not provide sufficient air flow and computers overheat often. Good computers will shut down before damage, but not all. Good luck!

You know I have to agree Swobovike. A friend of my had that problem and add a fan to blow air over the graphics card and it worked after. He even overclocked and it still worked.

I have tried everything like even changing my Hardisk and the cooler fans and nothing works.

,i have formatted my hard drive.and then installed a fresh copy of windows xp. but after the install my graphic card is not working. and i also dont know my pc model number

If you can run the v8420 in save mode (f8)
then check the voltages. Or check the voltages
in the BIOS at POST.
If agp voltage is too low, then must get a better
power. Some detail power on each rail of
5v 3.3v, and 12v.

Dear Friend, it seems that overheating is the culprit here. If possible, try installing a fan on the Graphics card.

If not, recude the clutter of cables around the card and invest in some good Cooler fans.

I would also recommend a VGA cooling solution from Cooler Master. Will cost you a couple of more bucks but will rid you of this issue forever.

I hope i was able to solve your issue because i faced the same issue and i got the resolution from some geek at ***.

Craigbest
Did you resolve this problem, as I have the identical problem.
I have a heatsink & fan on the card. I also have run my computer with all the covers off to increase air flow, but still the problem persists.