Or maybe something is not seated properly inside the computer. Maybe CPU's heatsink. When you move it around it fixes or breaks itself.
DING DING DING DING!!! WE HAVE A WINNER!
You hit the nail on the head my friend; After a closer inspection, I found the CPU heatsink more or less floppnig around! How the heck could that come unconnected like that? I replaced the Heatsink to be on the safe side and so far so good after ~ 1 hour. I'll deliver to my friend's house tomorrow. thanks!