Computer randomly black screening

[WillGrabham]

For nearly the past week my computer has had a mixture of freezing, and more recently black screening. My specs:

Ryzen 3 1200

8GB DDR4 Ballistix 2666 (tried using D.O.C.P profiles and not) (bought used)

Asus prime b450m-a

Gigabyte G1 RX480 (bought used)

Samsung SSD 840 EVO 120GB

EVGA 650W B3

 

I built the system at Christmas and it has been perfectly stable. I bought my RX480 used off eBay, and it looks like the BIOS wasn't signed so I used atikmdag-patcher-bios to sign the driver and it has been working fine. More recently the GPU always had it's fans spinning, which I thought was odd but maybe just a build up of dust, so I carried on and then the computer started freezing and I'd have to power cycle it. Now the computer has started black screening, believe the computer stops working when this happens, and the GPU starts spinning, then stops and this repeats. I took the GPU out and cleaned it (which took about an hour), and then put it back in; this then worked flawlessly for a day, with no freezing or black screening. It seems like when I leave the computer for a while with the PSU switch turned off, it seems to last longer after without freezing or black screening. 

I have tried memtest and both the ram sticks passed with no errors. 

Has anyone got any ideas? GPU Bios issue (have tried to reflash with no success)? Motherboard bios issue?

Thanks for any help

 

[homeap5]

You already diagnosed your problem, just don't like the obvious answer.

 

Want to be sure? Use some old GPU if you have any for few days.

[5x5]

You bought q fucked mining card sadly