Eddy
5
Ok, so no malware found and no dust.
It sure looks like a hardware problem.
I suggest you run several hardware tests.
Utils for it can be found at: http://www.carrona.org/hwdiag.html
With memtest, let it run a entire night.
Sometimes a memory problem only shows up after a while and not on the first cycle.
Disable power saving settings and screensaver before letting it run.
Did you take out all cards, cleaned the slots and contact points and put them back in?
It could be something simple as a bad connection.
Did you change any hardware lately?
Use this util to check how much power your system is consuming:
http://www.extreme.outervision.com/psucalculatorlite.jsp
PSU’s tend to give less power overtime.