Question PC shuts down instantly after starting a game

Oct 10, 2020
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Hello everyone, i recently bought this PC with a

ASUS Prime X570-P Motherboard
ryzen 9 3900x,
a thermaltake toughpower 850w
32GB RAM
and a rtx 3080 (has not arrived yet, so i'm using my old gtx 1080ti)

I first started having problems in Apex Legends, where the PC would just randomly turn off while playing and watching a twitch stream at the same time.
The shut down looks like this: Everything goes dark, except for the Power LED on top of the Case. I have to pull the Plug or turn the PSU off so that i can start again.
Now the problem got even weirder. i thought that it was a faulty PSU or the weird thermaltake silent fan mode, but i pretty much ruled that out, i did a 3DMark Stresstest for 30 Minutes with no shutdown and i did the TimeSpy benchmark also with no shutdown
I bought serious sam 4 to play with a friend, and everytime i boot that game, the PC instantly turns off with a weird noise coming from the PSU, which i never heard before, but the noise persists for like 3 seconds and then it turns off (it almost sounds like there is something stuck inside maybe).
I figured it must be software related, because i had absolutley no problems outside the game and in the stresstests
 
OKAY! it was the PSU, it's now completely broken. The PC does not turn on anymore, although the mainboard LED is still on.
never buying thermaltake again