I just bought a Dell XPS 8500 PC, which came with a GT 640 and Windows 8 64-bit. I replaced the PSU (stock is 460 watt) with a Dell Silencer unit (500 watt) which worked great for me in my previous XPS 410 system with a Radeon 4890 and installed an eVGA GTX 6600 Ti. When I just booted into the initial Windows setup, it went fine, but without drivers the resolution and colors were poor as you might imagine. I downloaded the latest drivers from eVGA and installed them. Upon restart, I got a black screen with the Windows loading graphic and then a black screen. Tried a few more times - same thing. So I restored Windows, got the same poor quality display and tried the drivers from Nvidia's website. This time I got one step further - the black screen displayed the white mouse cursor which wasn't moving with any kind of rhyme or reason. Hitting keys on the keyboard does nothing. I wrote to eVGA and they suggested I try the card in another system, which I will do today (I'll just plug it back into the XPS 410 - the 460 watt PSU should handle it fine, I just wanted to keep the better one). I have a sneaking suspicion that the issue is with Windows 8, but yet others had been able to do the swap without a problem. The XPS 410 has Windows 7, so I'll get to test that hypothesis, but I'd eventually like to stick to Windows 8, so a long-term solution is still needed. Any help would be greatly appreciated!
Oh yeah, this should probably be mentioned - the only "monitor" I have is a Panasonic Plasma TV which worked fine with the XPS 410/Radeon when hooked up via HDMI.