PC periodically “turns off”

I’m on a custom-built windows 11 PC (Ryzen 5 x570) and have recently been having an issue where the PC will become totally unresponsive; it’s still “on”, the fans and lighting still work, but it won’t output to the display and can’t be accessed remotely (Plex and TeamViewer both consider it to be offline). The only fix for this is a hard reset. I haven’t witnessed what happens to put it in this state.

This seems to have started after trying out the Curve Optimiser built into Ryzen Master in combination with PBO, as well as using the OC scan in ASUS GPU Tweak, which also affected voltage. The CPU OC has been reverted, so that seems to leave GPU, and I’ve dealt with weird PC behaviour related to cooling/OC with the GPU before (I haven’t been able to check because I’ve been out of town).

One strange bit about it is it’s seemingly random nature. It’s never entered this state under load; it only ever happens more or less at idle (my PC is on all the time because it doubles as my Plex server)

EDIT: I’ve removed the GPU OC from ASUS GPU Tweak, which had messed with voltage. So far the hard crash hasn’t happened again, but I’ll try to remember to update this again if it does occur, for the sake of future googlers

EDIT 2: It’s been about a month now and the issue still hasn’t occurred, so I’m pretty confident it was the GPU OC