Most likely cause is hardware, but without knowing specifically what the cause, the process is lengthy. Before trying to diagnose the specific computer problem, lets rule out drivers another potential cause Driver Verifier - Enable and Disable
Read the instructions for verifier, if you followed the instruction precisely, we will move on.
Remember, if we are wrong with the driver analysis, we may never find the cause if it is indeed a driver.
Theres a problem, here. The memory test, alone takes hours. You could not have done them all so quickly. Follow these instructions for the memtest.
Run for 8 passes.
Then test each stick in a good slot for 6 passes.
If you have dual channel, the results may be incorrect, if shows pass. Guide to using Memtest86+ - Geeks to Go Forums