What you're looking for will be in one of the following categories:
a) BIOS bug
b) a driver whose activity is causing the target processor to lock up
c) a hardware defect (temperature, voltage, dust, RFI, outright borkedness...)
Prime95 Setup:
- extract the contents of the zip file to a location of your choice
- double click on the executable file
- select "Just stress testing"
- select the "Blend" test. If you've already run MemTest overnight you may want to run the "Small FFTs" test instead.
- "Number of torture test threads to run" should equal the number of CPU's times 2 (if you're using hyperthreading).
The easiest way to figure this out is to go to Task Manager...Performance tab - and see the number of boxes under CPU Usage History
Then run the test for 6 to 24 hours - or until you get errors (whichever comes first).
The Test selection box and the stress.txt file describes what components that the program stresses.