[Radeon] 9550 128Mb problem

Question

Hey there people, I bought an MSI Radeon 9550 graphics card recently and, well... it just doesn't work properly.
It boots up fine and everything, all my programs run fine except for any graphics intensive ones - basically computer games  .
I've tried everything I can think of short of reformatting my HDD (and I doubt that would work) I've uninstalled and reinstalled drivers, for both Mobo and for Gfx, i've reinstalled windows, put my old graphics card in to see if it works fine, it did (A Hercules Prophet 4500  ), then uninstalled its drivers, took it out and put the Radeon in, installed drivers, still wont work properly.
When I first got it within about 5 - 10 minutes of gameplay I got the error "VPU has reset your graphics accelerator because it has stopped responding to the graphics drivers commands". Now the PC just crashes and it doesn't even bother with the error message. I've taken it back to the shop where I bought it, they ran it on their system and tried everything they could to get the same error, they tried it on 3Dmarks and it ran fine and basically i'm just stumped what to do next. I've checked in system or wherever it is (i've forgotten) and it says that the Graphics Card is running fine with no faults. 
My system is as follows:
Mobo: ASRock K7V88 VIA Chipset
RAM: 4 x 256mb Kingston 400mhz
Processor: AMD Sempron running at 1.66ghz
If you need any other system details just ask and i'll tell you
Cheers, Walty

Answer 1

Could be leftover driver bits from the previous card. Not to mention the possibility of a corrupted registry and/or hardware table.
I would try the card in another PC to check if the problem follows the card. Then consider a complete format and install depending on the results. Perhaps try experimenting on older drivers for the VGA and the chipset as well. For all we know there could be a compatability problem.
Not sure if "Driver Cleaner" would help in this case. http://www.drivercleaner.net