I've recently put together a new machine and I've an interesting conundrum that I've not encountered before. I'm using the P7P55D Pro along with a 1Gb Palit 9800GT and 64bit Windows 7 Pro. The issue is with the graphics card; windows is only reporting back 440mb of video memory, and worse, I appear to be completely unable to install drivers for it; attempts yield the machine crashing to black screen and blinking cursor. I will be able to test the card in an alternative machine in the not too distant future - but has anyone seen this sort of issue before, and if so, can they please advise?
Apparently, I can't edit my previous message - anyway as an update, the card itself is working perfectly fine in an older Vista 64 machine, so I think we can rule out the issue being with the card itself.
I had similar problems with my 9800gt and a p7p55d motherboard. The computer would stop responding during windows 7 x64 boot up. Safe mode appeared to work OK. It took me a few tries to even get windows installed. I had no problems in Ubuntu linux. I replaced the card with an nvidia 260 series card. No problems since. My guess, there is an incompatibility with Windows 7 x64, the p55 chipset and the 9800gt. I put the 9800gt in my older system running Windows 7 x64 and it runs fine there.