In my bios my +12 rail appears at 12 volts.. So I think there is no problem. It appears at 8 volts on HWmonitor.
I have a new clue! While playing League of Legends, my screen turned black and it crashed as I described. But, after restarting and entering the game again, after 10 minutes the screen went black (like when it crashed) but it came back to the game after 2-3 seconds! What could cause this?? GPU faulty? PSU faulty?
After that I checked my minidump files. I was able to find two drivers
that could be involved in the crashing (maybe, or the last drivers that was detected before crash): nvlddmkm.sys and dxgkrnl.sys.
Now, I connected my GPU and RAM in other slots to try. Maybe these slots were bad or maybe the components were not correctly connected.