In the last week I have put together a completely new build with the following specs
Asus ROG Strix B550
Gigabyte 3070 OC
2x8GB Kinsgston Fury 3600Mhz
WD Blue 500GB NVME
Gigabyte 750W gold
System boots up into windows fine and browsing the web etc comes without issues. However whenever I fire up a game it completely shuts down, No BSOD etc, just a complete shut down as if its overheated. It can only be turned on again after removing the power plug for a short period.
I have run various scanning programs to log the system temps etc, the last shut down it did so with the GPU at 46 degrees, CPU at 63 degrees so all well within temperature tolerances. I've run corecylcer overnight which threw up no errors and I am wondering now if the CPU itself may have an issue (I have tried reseating it.). Also ensured that all cables are plugged in correctly, double checked multiple times
I had a similar issue with one of my rigs. I updated all drivers (windows, AMD) , ran sfc /scannow and chkdsk /F. I even reloaded Windows a few time. It ended up being PSU... On a suggestion I upgraded from a 850 to a 1600 and everything ran great.
It doesn't sound like a cable issue to me, because it posts fine. And it looks like you ruled out temps. I would guess a PSU or software issue. Hopefully someone smarter then me comments though, lol. I'm definitely not an expert.
Download the freeware OCCT and run the PSU test and see if it shuts down during that test or any of the other two tests - CPU and GPU.
During the testing keep a close eye on Temperatures, Fan speeds, and especially PSU Outputs 3.3/5.0/12.0 Vdc.
If any PSU outputs goes below 5% during the testing, especially the 12.0 vdc, that indicates a failing PSU.
According to a CPU & GPU - PSU requirement website it says this about your CPU and GPU and PSU:
You need a power supply with at least 550W
NOTE: When a PC shuts down without powering off that indicates:
Overheating, Power, Overclocking issues, RAM issues (defective or incompatible), Driver issues, Defective hardware issues are some of the main reasons.