Question Sudden intermittent strange crashing behavior, PC powering off and not turning on until flipping PSU switch (some troubleshooting steps taken)

[FirionHope]

So I tend to leave my PC on overnight, I wake up a couple days ago and its off. Furthermore, it won't turn back on. I try messing with the power switch and plug, no dice. Play with ram configurations (removing one, reseating, trying a stick from a different system, etc.) and sometimes it'd come on for a couple minutes before turning off again, hard shutoff and usually won't come back on (as in when I hit the power button literally nothing happens) unless I unplug it or flip the switch and wait a few secs for the power to drain or something. Often would shut off before even getting to the bios. Sometimes the ram problem led on the mobo would come on but considering I tried multiple configs including using a stick from another working system and that it would only occasionally happen I'm not convinced it's related. Though when I put the new stick in I never did change xmp values or anything, I assume they'd default to off with a new stick? I also tried replacing the power cord of the PSU itself but it didn't seem to change anything.

So anyway. I figure it's probably a PSU problem, I pull one from my backup PC and after a long and painful process (5 hours including messing with the ram and trying to diagnose it) get it hooked up and going. It then booted up and worked fine for the rest of the day and until near the end of today. I monitored temps for a bit but didn't see anything out of the ordinary. I did notice a while before it crashed my game seemed to be hitching more than normal but its an emulator for a modernish system so it didn't have the most stable performance to begin with, can't tell for sure if it was worse or not but it seemed like it.

But suddenly when I was playing for an hour or two it hard shut off again randomly with no warning. And then wouldn't come back on once again until I turned it off via the power switch long enough for whatever mobo led lights or whatever to turn off. When it came back on it went through and repaired one of my HDD drives, also said it repaired my F drive which is a virtual mounted drive with a game installed on it...

Probably a good time to mention too when I hooked up the new PSU at first it wouldn't detect one of my HDDs that had worked fine before until I replugged it on both ends a few times, scanned it with dskmgm afterwards and it didn't show any errors (different drive than the one that got repaired). Don't think it's related but worth covering my bases I suppose. Also as a note I ran sfc/scannow on a whim after the latest shut down and it did find and repair some files but again the issues start with it not even turning on at all with the power button or randomly shutting off in the bios so I don't imagine its a windows problem.



So basically I'm just wondering what troubleshooting steps to take next, if anyone has any ideas of the most likely culprits. I have a spare PC to pull from with a compatible mobo and CPU (though the mobo might need a bios update which should be doable with the other PC if I hook it up with a PSU again). I also have a couple spare video cards around, could it even be the Video Card? That would be the simplest swap but I wouldn't imagine it would cause hard crashes or non booting? Or maybe it can since Ryzen doesn't have Igpus? With this behavior Should I try the backup mobo, or the backup CPU first? Could it be something like a faulty wall socket or power strip? Nothing else randomly shuts off, (except my mouse and keyboard sometimes) but then again nothing else draws nearly as much power. My PSU does face downwards and its on carpet (I do clean the filters every so often) so maybe it could be a cooling issue of some kind? But weird that the other PSU would be fine for a ~year if so.

Specs
CPU Ryzen 3700x
Motherboard: ASUS TUF GAMING B550-PLUS ATX w/ RGB
RAM 16GB (8GBx2) DDR4/3200MHz Memory (Team T-Force Delta RGB)
CPU cooler: default wraith cooler
Video Card EVGA GeForce RTX 3090 XC3 ULTRA GAMING
Power Supply: 850 Watts - Enermax Revolution D.F. series 850Watts 80 Plus Gold Full-Modular (now EVGA 850gs, some older model from 3-5 years ago)
Hard drive(s): Boot: Sk Hynix Gold P31 1TB m.2, Others: WD Blue M.2 1tb, WD Black 1tb HDD, Toshiba 3TB
Operating System: Windows 10
Case: Phanteks Eclipse P400A (ran with side open)

Sorry for the wall of text, hopefully I mentioned everything important.

 

[Cyberat_88]

If you still have the time to RMA the PSU, do it first.
Leaving the system on 24/7 does eat up your HW lifespan hours & exposes your system to brownouts, shorts & other anomalies, as well as hacking.
PSU & HDDs will be the first to go in this scenario, no idea why you still use them inside a system with 2x M.2s.
If you invested that much in a computer, I strongly suggest a UPS system. (https://www.bhphotovideo.com/c/search?Ntt=cyberpower ups&N=0&InitialSearch=yes&msclkid=c326ed166e7a1e494fdd8fc020c00851)
Granted moving backup HDDs to USB3.0 enclosures, you'll lose some speed, but not enough to warrant early death.
Keep in mind your printer(s) power consumption when you buy a UPS, laser printers consume more (if you want them on the battery side).

 

[FirionHope]

If you still have the time to RMA the PSU, do it first.
Leaving the system on 24/7 does eat up your HW lifespan hours & exposes your system to brownouts, shorts & other anomalies, as well as hacking.
PSU & HDDs will be the first to go in this scenario, no idea why you still use them inside a system with 2x M.2s.
If you invested that much in a computer, I strongly suggest a UPS system. (https://www.bhphotovideo.com/c/search?Ntt=cyberpower ups&N=0&InitialSearch=yes&msclkid=c326ed166e7a1e494fdd8fc020c00851)
Granted moving backup HDDs to USB3.0 enclosures, you'll lose some speed, but not enough to warrant early death.
Keep in mind your printer(s) power consumption when you buy a UPS, laser printers consume more (if you want them on the battery side).

Well as I'm having the exact same problem with a replaced PSU I'm thinking its unlikely to be a PSU related problem
HDDs I use because I like to have a lot of storage at an affordable price, something SDDs still aren't nearly as good at.
I do indeed intend to buy a UPS sometime and appreciate the advice, however money is tight atm, and I have more pressing concerns such as the randomly crashing issue I'm dealing with, which means at least one thing needs to be replaced as I like to have a backup PC to pull from for situations such as this.

 

[JEM_1997]

I'm interested to know if you ever discovered the culprit as I'm having the exact same issue right now. I already tried replacing the PSU and it's still hard crashing with no warning. Seems like the power is just cut.