I, like Dale, would lean toward hardware failure. I would have suggested memtest86 (tells you how old I am) an old DOS utility that I used to use to diagnose intermittent memory failure. After a quick search I found
http://www.memtest.org/download/2.01...+-2.01.iso.zip
Seems someone else liked it too and has been updating it to keep up with new CPUs and chipsets. Burn it to a disk and boot from the CD. That way you don't introduce anything to your pristine computer.