I disconnected everything and connected the power rails. I still get a strike from the motherboard ground!
It's either the motherboard or the PSU. But I think the PSU could be OK.
One thing I have to mention here, is that this PSU failed before months, and the problem was with the 12V power MOSFET. It wasn't working at all because the 12V rail is feeding the 5 and 3.3V rails. So I replaced the MOSFETs and it worked like a charm.
But there might be a possibility that there could be another problem or other broken components I wasn't aware of.
Or the motherboard, this motherboard actually took a hit during airflight shipping process, and the my first gpu gtx 770, wasn't screwed. So the gpu got off its slot and was rolling inside the rig all the time of that shipping, of course when I recieved it, the gpu was broken and there is a problem with the fans pins, one of the fans ports doesn't boot at the same time of the other port, it take a delay then the fan LEDs launches and the fan spins.
This is my current setup.
I need a PSU, to test this rig, but the problem is that in this city there are no famous places where I can test it! Maybe I can try and take the motherboard only to test its short, I think that would be the best solution to figure out which one is causing the problem.