PC won't stay on, shut off suddenly after boot, no more response

[GooeyGUI]

This PC idles day and night for many years so far. Today, it was turned off to reduce heat because it's 106 F outside. Five hours later, it was booted into windows and a program (MUSH client), and then it just shut off. It won't turn back on and there's no light in the case.

I'm very suspicious that the PSU has gone out. I do have some old PSU's around that might work with that PC, but in this heat I was hoping for a break.

I wasn't quite ready to upgrade this system yet, so it's really poor timing when I have a new case already but nothing else to go with it. I have spent zero time on reading up on suitable CPU/ mobo /GPU(s) reviews.

Could it be something other than the supply?

 

[Eeqmcsq]

No, that really sounds like a power supply issue if you don't see any lights of any kind from the motherboard.

 

[Modelworks]

It is rare, but it could be the power button itself.