Try powering off the power supply, disconnecting the HD power cable while leaving the SATA data cable connected and turn the power back on and start the PC. Watch for the post screen and just when you see it detect the HD power off the pc, reconnect the HD power and start it in the normal fashion...
I had the same problem as well as many others...if you ask me the southbridge is deteriorating. I just scrapped out my mobo that is listed in my sig and salvaged all other parts for a home server.
If I were you I would cut your losses now and just move on. I must have installed XP a dozen time in a month while troubleshooting thinking it was a driver related issue...it will never get better.