I'm Sam, 72 retired manager; only became interested in computers at 65...recently completed third self build and having trouble with BSOD 0X00000012 and when I searched for an answer was led to this site. Not solved yet, but learning.
With relation to your BSOD, what OS are you running (windows 2000, xp, vista) and which service pack?
Generally that error means a bad 3rd party driver. Try booting in safe mode and seeing if it occurs. If not then you know it must be a driver problem (in safe mode only core Microsoft drivers are loaded)
Try safe mode. If the error doesnt occur in safe mode then boot into normal mode (but remove all non-essential cards and peripherals) and see if it happens. If it still is fine then add the peripherals one at a time until you find the one causing the problem.