PC turning off a few seconds after starting game

PFA

Greetings all. Basically I’m having an issue with my older build that’s been giving me trouble as of recently.

Basically any game I play or launch causes the whole system to shut down and reboot.

I get no error codes or blue screens but I’d figured I’d ask here to see if I’m missing something?

Here’s my specs

Intel I7-7700K

1080Ti SC2

32GB Corsair Vengeance

RM850 PSU

I have an AIO for the CPU but the temps seems fine.

2- 2TB SSD’s

I play in 1440p but I’m not sure if it’s a GPU issue.

Here’s the things I’ve done so far:

Drivers checked. Uninstalled and re-installed.

Windows re-installed

Steam library re-installed

Tried moving games to different hard drive.

Tried lower settings

Ram Diskpart or the disk check multiple times

Ran memtest multiple times.

As far as I can tell the only time I have issues is when launching/ starting a game. Once I’m in said game the PC crashes within a few seconds all the way to black screen with no warning. I’ve had no issues with this build for years really and now it just started.

Any help would greatly be appreciated 🫡