Question PC crashes after 15 minutes; does not turn back on

Sep 2, 2020
I have been having this problem for about three months.

When I boot up my PC, everything starts up normally but then around 15 minutes in, the entire machine shuts off, right to a black screen. Upon trying to boot up the machine, it power cycles and I can't get it to start up. I have to wait about a day before trying to boot it up again, and it DOES boot up normally but then it shuts off in the same way as I mentioned earlier. I have been using my laptop for awhile now to compensate but since that recently failed, I need to use my desktop normally.
I built the PC in March, 2020 and the problems started around September, 2020. I have posted on multiple forums but no one has been able to find a solution.
I am pretty savvy with computers, but can't figure this one out. My first guess is that it's a failing power supply, but why would it randomly shut off when idling, when, under full loads, it's fine. I thought it was a software problem but I wiped the HDD and reinstalled windows and the problem is still persisting. Also, why the power cycling?
Any help would be appreciated because at this point I am pulling my hair out.

Here are my system specs:
CPU: Intel i9 9900k
GPU: 1080ti
PSU: Corsair AX1500i (6 years old)
Cooler: NZXT Kraken x61
RAM: Gskill TridentX 32gb DDR4 2333Mhz


6 years is a long time to hold onto a PSU. I'd ask you see if you can source a more concurrent, reliably built PSU like one by Seasonic to see if the issue you have with your system is resolved. Have you tried disabling Deep Sleep state in BIOS? It's listed as C6 but that will be detrimental towards your platform, since it will need to cool harder.

I'm looking at a PSU problem, since the standards for what PSU's need to be capable of delivering have changed somewhat with concurrent hardware. Make and model of your motherboard? Why do you have DDR4-2333MHz rams paired with an i9-9900K?