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.