PC randomly shuts off, seemingly unrelated to temps/load

[Freddy1765]

I'm having a peculiar issue with my desktop where it will randomly shut down, and I can't figure out why. My PSU is an EVGA Supernova G2 750W, which I believe is quite a good model. I don't remember when I bought it though, could be anywhere from 3-5 years old. Rest of rig in sig, should be 5 years old this August.

What's puzzling is that it doesn't seem to matter whether the computer is under load or not. A few days ago I was running some simulations where my 4790k was running 100% utilization on all threads for 10+ hours without issues - the next day the PC shuts off while I'm not even using it. Temperatures are definitely not the issue either, I've made sure of that.
Winows does not produce a BSOD or any kind of error message, the PC simply shuts down and I have to push to power button to boot it back up. I think the issue started a few weeks ago, possibly after I formatted and re-installed Windows 10.

I've never experienced a failing PSU before so I'm not really sure what kind of signs to look out for. How do I troubleshoot? I do not have spare parts lying around to replace things one at a time.

 

[UsandThem]

Sounds like a failing PSU to me. However, first remove any components that aren't needed for the PC to work (OS drive, 1 stick of RAM, use integrated graphics on CPU, removing GPU after changing that in your BIOS, and shutting down PC).

That PSU has a 10 year warranty if registered with EVGA (could be 7 years, I'd have to look).

What way does your PSU fan point (up or down)? If facing down, disable the "eco" fan stop feature as heat builds up in PSU with no place to go, and can shorten the life of the unit.

 

[Freddy1765]

snip

Good advice, I will try and remove some components.

I don't think I registered the PSU when I bought it, not even sure if I still have a receipt. I'll look for it.

The fan points down and I have eco mode enabled. I actually bought this unit specifically because the fan turns off at idle. Perhaps I should try and flip it around instead, or I could disable the fan-stop for a few days to see whether it has an impact.
I will say that the parts of the case surrounding the PSU aren't warm at all, though I don't know what kind of fan-curve the PSU operates with.

 

[Almighty_Denny]

It may be unrelated to hardware component temperatures, but NOT to actual PSU temperature.

You should check out if your PSU is not overheating.
Even something simple like a loose fan cable inside the PSU could cause thermal problems.