10-14-2016, 09:00 PM
Very intermittent failures like that (when not overheating) usually indicate a power supply or motherboard issue. As you already tried a different power supply I would say BGA failure on the motherboard due to age and heat...
Asus N55SF, i7-2670QM (~2,8 ghz under typical load), GeForce GT 555M (only OpenGL)