Let's see if we can use Windows "verifier.exe" to catch the culprit.
Before using it I want you to confirm that you can start to and restart from Safe Mode. Not everyone can do this, as some folks with video driver problems hang on a Safe Mode boot.
Instructions on how to boot in Safe Mode here:
http://service1.symantec.com/SUPPORT...01052409420406
There is a detailed article on verifier.exe here:
http://support.microsoft.com/default...b;en-us;244617
However the short and skinny of it is, you simply go to start or open a cmd interface and enter:
verifier
... and accept its default options. On reboot it will run, and run on every reboot until disabled by the command:
verifier /reset
If you get a STOP error you will not be able to boot in Normal mode until you reset verifier, so you MUST be able to do a Safe Mode boot.
If you do get a STOP error, look for the driver mentioned. The actual error parameters here will a STOP message for verifier, and will not shed too much lite, but you can copy it anyway.
AND although it won't stress test any drivers, like "verifier" you can also see what "unsigned" drivers you have on the system.
To do this go to start and run
sigverif
Unsigned drivers aren't necessarily bad, but in this situation they might bear some extra scrutiny.
Also, if neither the ram tests nor verifier.exe turns up anything, post a HijackThis Scanlog so we can rule out any obvious malware issues:
Download and install HijackThis using the "self extractor". Run it and select "do a system scan and save the log file". Then copy/paste the contents of the log to a reply
http://www.thespykiller.co.uk/files/hijackthis_sfx.exe