FINAL UPDATE: I've just stressed CPU + RAM + GPU + HDD at the same time with HeavyLoad software, everything is running stable, played some A3 with GTX750Ti on OC mode and attempted to record on the fly with shadowplay for 5 minutes, no problems at all so far. Steps I've taken before fitting MoBo back to the case before it actually started to work perfectly:
1 - As you may know I've removed the MoBo to clean it up and find anything unusual. After trying it out of the case it wasn't working properly so I assumed I had run out of options here other than just get rid of the MoBo, sell the CPU and buy a new combo LGA1150.
2 - I have tested the PSU with a multimeter, the values are perfect and no fluctuations at all, so I've decided to search for some info about the VRM, especially MOSFET's.
3 - I've seen a tutorial of how to test a MOSFET resistance, so I've just gave it a try, the MoBo was practically unusable, but I was willing to fit it again onto the case and stress it to the point where it would smoke. Ok, so I've just tested the MOSFET's to measure the resistance and I had values on all of them but they were very different from each other.
4 - It can be just a coincidence but it makes me believe that some static electricity was storaged inside of one or more MOSFETs and it was discharged when I touched the probes on the pins.
5 - Please notice just for future reference, I am NOT sure if the MOSFET's were the real problem, all I know is that after I've tested them and attached the MoBo back to the case it started working perfectly just like that, magic and weird at same time!
I will mark this thread as solved as I ran out of options here, unless some other symptom comes up, I won't hopefully come back to this thread.
Many Thanks everyone:thumb: