Computer problem started after started the computer but did not actually USE it so I just turned it off or cut the power. Before this I have [XP Pro w/Sp3 on my 30 GB hddrv and Win7 on my 200 GB that were WORKING properly. Upon starting the very next time Win7 would not load, the computer booted up till it gave me the choice of picking Win7 or reverting back the O/S to a previous version. I have been using Win7 but this time it would not move out of the boot sequence. When I chose Win7 or XP it stopped. I watched this for about 2 wks.   I was very confused as my computer problem, I took everything out, why you ask, I don’t know. Anyway I reinstalled a previous MB (p4p8x), It appears it doesn’t work, It showed no indication that it would work, So I took it out and put my p4p800D-X back in as I knew that It worked before, but now it quits during the post procedure. I used a pci posttest CARD, still installed, its readout gave a FAULT reading [d3 and possible 0110] readout. That’s  where I am know.  As I reread my post- I forgot to list the first good working MB was a P4P800D-X which worked great till the above problem showed up. Igave up on the P4P8X MB put back theP4P800D-X in which is where my {problem REALY started}. My first thought is RAM. I didn't lookup those mobos, but did you keep all the other components the same? Same CPU, video card, etc?