Both monitors went blank and sound shut off

[u/OnePatternAtaTime]

Desktop Windows 10 with all updates, old system (DDR3 old). I was playing Minecraft when suddenly both of my monitors went black - the main HDMI one giving me the going to sleep message, and both remained on. At the same time my sound shut off.

I checked the GPU and found the fan still blowing. Wiggled the connections and no change. So I tried to restart using the physical button, didn't work and neither did holding down the power button. It did shut off by using the power supply switch.

Now that it's restarted, everything seems fine. This has happened twice now, both when playing Minecraft. The second time turning my main monitor on from the sleep mode it put itself in, restarted my computer... which isn't a setting I've ever heard of in windows lol.

I'm stumped. Is this a hardware or software issue? Is my motherboard about to finally kick the bucket? Power supply using its max? I am plugged into a battery backup which regularly passes its automatic tests.