Weird graphics card issue - ATI HD4830

Hi Guys,

Wondering if anyone can help me out here. About a week ago my wife   started getting weird distortion on her PC at all times - from post screen right up to Windows running. There would be vertical lines on the screen, odd pixelation etc which got worse and worse until the computer would no longer boot. At the time she had an NVidia 8800GTS installed and an MSI MS-7184 mainboard with AMD slot 939 processor and 650W PSU. The PC had been working adequately for years prior to this incident.

Removing the graphics card and booting up with onboard graphics fixed the weird pixelation and enabled windows to boot, so I instantly assumed that the graphics card was going faulty and bought a slight upgrade - ATI Radeon HD4830.

This seemed to fix the problem to start with, as there was no pixelation, and Windows booted up fine. However we began to experience random crashing, where the screen would go pixelated green, and then freeze the computer.

This was irritating to say the least, so I decided to swap the graphics card over to another PC to see if the same thing would happen. As it happened I had to switch the hard drive over as well, as the other pc had Ubuntu installed and I wanted to keep the test fair, and also the PSU as the one in the other PC was only 400W and had no 6-pin connector. The PC didn't boot at all - it got to the Windows loading screen, and looked as if it would work, but the screen went black after Windows loading screen, and the graphics card fan spinning like crazy. I swapped the PSU back out for the old 400W one and used an adapter to created a 6-pin connector, and exactly the same thing happened. So as far as I'm concerned this rules out a faulty PSU (?).

I then switched the PSU back to the 650W one and formatted the Windows hard drive with a fresh copy of Windows 7. So, now we have PC2s (Gigabyte) motherboard, 1gb DDR2 ram, AMD AM2 processor, but same PSU and formatted HD from PC1, and still the same thing happens.

So, to summarise, the PC still boots 100% fine without the graphics card in place. With the graphics card in place, the PC doesn't get past the Windows loading screen, and the graphics card fan spins wildly out of control and sounds like a jet engine. The same fault occurs on 2 different motherboards with 2 different processors, RAM, PSU etc.

The strange thing is that I can see the POST screen, and I can see the Windows boot screen so the graphics card isn't completely dead. However, having said that, have I been sold a faulty Graphics card do you think, or is something else at fault?