I'm no expert, but it sounds like you are checking the correct things.  That error can be caused by memory problems, overheating due to dirt build up, a virus, a bad psu, and I believe even power surges.

 

It is unlikely that you have done any damage to you system running the tests.  If you want critique on the procedures you are being asked to perform, it would help if you provided a link to the topic.

 

The bottom line is, there is no simple solution and it is even possible that you will never find the cause.