So tell me what new paste is going to do to fix a blue screen. It is for filling in the cracks and uneveness for better contact with the cpu and heatsink. So even old or even none as some I know do, it should still keep the cpu cool. At least to boot up.

It sounds to me, as a guess, more like the cpu has been un-seated from the motherboard. It is a common problem when removing the heatsink. That old paste can be a pain to break the seal. I have read many threads on this happening.

Maybe try pulling the cpu out and resetting it back in. Check for bent or broken pins. You can set the heatsink on without paste for a test. To see if you can get it to boot up.

As for the nvidia card, I just picked up a gtx460 1gb for $150 on sale and with the latest drivers it works great on both my xp64 and my win7 64. I had to decide which computer to drop it in. I finally decided the little extra and faster ram was better in my main machine, xp64. Vue infinity loves it and so does my Modo. That left me with my gtx260 to drop in my win 7 64 for my DAW and video editing software.

Sorry to hear you have problems and it is caused by the new graphic card. Sometimes things just don't work in some systems. Hope you can find and correct the problems.