Why did my computer randomly stop working?

So, I was just playing a shooter game, and my computer randomly shut down. No blue screen, no error message. It just straight up turned right off.

I am now unable to turn my computer on. As far as I knew, the computer was just fine, and still is. All the cables are properly plugged in, switches and whatnot are all on, even the lights on the back of the computer (where the Ethernet is plugged in) are still working... but I can't power it on.

I am at a complete loss. I don't wanna start taking my computer apart without some ideas as to why this might be happening. I know it can't possibly be the power supply, that would mean everything wasn't working, and there is definitely a light on in the back. And if it were a drive, then I would have likely received an error, and would still be able to turn the computer on, just not boot to the drive.

Other than a power supply or drive failure, I can't even think of what might be causing this.I spent about 20 minutes poking and prodding every viable inch of my computer, fiddling with cables in and out, seeing if maybe something was loose somewhere. I've never had something like this happen before, and I've been through 4 or 5 computers with numerous issues spread out over 20 years of living. This is the WEIRDEST problem I've ever had, swear.

Please (very much so) and thank you for any help!