Graphics card in 4x and troubleshooting motherboard

[Mozes]

So about half an hour ago, i  was playing CS-GO and suddenly, screen went black. At first it looked like the power went out but that was not the case. after a few seconds, youtube video started playing (screen still black (and by black i mean black except for a white line across the top part of the screen)) and the coolers started blowing really hard. Rebooting didnt fix the problem, i tryed different 6 pin connector, unpluging the card and puting it back didnt help either. Then i put the card in 4x slot on my motherboard and everything seems to be working just fine (games are running still really well, and even Tensor flow is working).

My question is what is wrong? Can it be GPU? Can it be CPU? or is it just bad PCIE 16x slot? How do i find out? Everything is under warranty but i built the pc myself so i need to identify the faulty part in order to use the warranty. 

 

board - GIGABYTE Z270-Gaming K3

CPU - Intel Core i5-7600K

GPU - GIGABYTE GeForce GTX 1060 WINDFORCE OC 3G

ram - HyperX Fury Black 16GB (2x8GB) DDR4 2133

PSU - Seasonic S12II-620 620W