https://www.google.com/search?q=RX+480+8GB+black+screen+crashes seems to point to GPU issues.

Go over the priors and one last thing.

If you overclock, then ALL BETS ARE OFF. This area can sorely confuse the new users. Overclocking is never a sure thing. You don't know what will happen. This is why you don't see me complain or even tell about a failure when I tried overclocking.