Question Possible GPU malfunction (not completely sure just yet)

[SuicidalSmoke]

so this issue started about a week ago. at first it was very random and happened even in apps like google chrome, however the first time I launched a game, It happened instantly and I knew there might be a pattern there. basically what happens is that each and every time I start a game, any game, everything just dies. "dying" may not be the proper way to put it, but I don't know what exactly is happening. the case is still turned on, the fans spin, the LED's are fine, the power and restart buttons both work, but I have no sound, picture or control on any of the external devices. what seems to be happening is that all of the external ports including but no limited to USB, HDMI and AUX just shut off. I have spent the last couple of days doing everything I possibly could to fix or locate the source of the issue. I changed my windows, benchmarked the GPU and the CPU and I got windows memory diagnostics to check my ram. on paper, everything is working properly, the issue however, persists. I talked to numerous people, tried all the fixes suggested on the internet, worth mentioning that there's nothing identical to what i'm experiencing, nothing worked. I was about to change my PSU when one of the guys I had spoken to called me. He gave me the most disturbing and yet only logical-sounding explanation as to why this is happening, but I'm not yet quite convinced. he told me that my GPU chip is hurt somehow, which causes the GPU to crash, hence putting the motherboard on a "fallback mode" as he called it, shutting off all the ports to avoid additional damage to any of the other parts. sounds logical, my problem with this is that I had already benchmarked my gpu more than once, using Furmark, and this didn't happen, except for of course when I launch games. which seems a bit off to me because Furmark is supposed to put as much pressure on the GPU as the games. or at least close which is enough for a faulty GPU to react. something else worth mentioning is that the day before this issue started happening, there was a regional power out, which could have caused something to happen to the PSU but I really doubt it because it was working just fine for like 7 or 8 hours afterwards. you guys are my last hope. all help is appreciated.
my rig:
motherboard: asus prime b450 plus
GPU: sapphire nitro plus rx580 8GB
CPU: ryzen 5 2600x
ram: kingstone hyperX fury 2*8GB DDR4 2400mhz
HDD: WD blue 2TB
SSD: WD green 256gb
PSU: Green 850W overclock edition

Update: I ran the same tests (games) with a different GPU and a different PSU. the problem persists. still no clue what might be causing it.

 

[rgd1101]

what the make and model of the green 850w psu?

 

[SuicidalSmoke]

what the make and model of the green 850w psu?

on the PSU it says Model : CP850B-OC