I've been struggling with this problem for two days, and I haven't found a solution so far...
So, two days ago my PC got a BSOD, without any prelude. (It pointed to usbohci.sys.) I restarted, then chose the repair option. It started loading files, then hung on the 'Starting Windows' screen. Couple more attempts, same outcome. Safe mode loadup stops at classpnp.sys.
Then I booted it from Hiren's Boot Disc, and (after 3-4 BSODs) managed to load the mini XP. I could save some of my data at least...
Restart again, trying to boot from Windows 7 Dvd. Nada... Hangs on "Starting Windows' again. Once it started somehow, I chose startup repair. It scanned for about half an hour, and came up with "Sorry, I'm unable to repair..." Another reset. Now Windows 7 booted up somehow! The desktop came up, seemed to go ok for about an hour. Then another BSOD. Memory dump something...
Since then it can't boot again. Same symptoms as above. Plus sometimes it shows another BSOD, with a bad pool header message. I hope I didn't miss to mention anything.
I've updated the BIOS, unplugged all unnecessary USB devices...
4 GB Kingston DDR2
1,5 TB WD S-ATA HDD (3x 500 GB partitions)
ASUS EAH 4870 512 MB
Win 7 Ultimate x64