Question Sudden shut off

[Geesise]

My PC has been turning off after a few hours of use and will not get to windows in a stable state for a few hours after it has turned off.
I know that it is not caused by overheating as it will still suddenly turn off even if none of the side panels are on.

I logged the turn on and off times for one day
8:30 turn on
11:40 sudden turn off
12:30 turn on
3:00 sudden turn off
7:30: turn on
11:00 normal shutdown

I built the computer 3-4 years ago.
Spec:
Asata Su360 240GB
AMD Rx480 Sapphire Nitro
AMD ryzen 2600
ASUS prime B450M-A
2x kingston value ram 8192MB 2666MHZ
Windows 10

I took it to a computer repair shop and they told me that the issue was a faulty SSD so i got a brand new crucial MX500 and replaced it myself, this did not fix the problem.
I have done windows Memory test on RAM twice and both showed no errors
swapped ssd to new crucial MX500, sata port 6: failed to get to windows desktop
added SU360 ssd to sata port 1: failed to get to windows desktop
unplugged MX500 and attempt to boot from SU360 : failed to get to windows desktop
unplugged psu from wall waited 10 sec, plugged back in and attempted to boot: got to windows desktop fine
prime 95 torture test: ran for 3 hours with no problems
swapped SU360 for MX500 and attempted to boot: failed to get to windows desktop, windows install looked broken.
attempted to reinstall windows on MX500: sudden shut off during reinstall
swapped back to SU360 and attempt to boot: got to windows desktop fine
Now I can get to windows desktop every time but after 5 minutes the computer will suddenly shut off
I am unable to check event viewer as the PC shuts off before i can read anything
I have never had an issue with getting to bios but sometimes SSD will not appear in bios.

I assume that the issue is with the psu or motherboard and would be grateful for any advice.

 

[Darkbreeze]

What is your EXACT power supply model and how old/how long in service is that unit?

How did you get the Windows OS from the old SSD to the MX500 SSD if the system isn't working correctly? Did you use a clone process on some other system and if so, what did you use to clone it and exactly WHICH partitions did you include?

What is your current motherboard BIOS version?

 

[Geesise]

the PSU is a cooler master mwe gold 550w fully modular model: MPY-5501-AFAAG and i have had it for 3-4 years.

the windows os on the MX500 is a new install from a USB that i did in one of the 3-4 hours that the computer was stable.

the bios is PRIME B450M-A BIOS 1820.

 

[Darkbreeze]

I mean, it's not the worst power supply ever. It's definitely not the best. It certainly COULD be the power supply, I am never against that because it is very often exactly what is wrong, and with the time component involved it would certainly seem as though it COULD be a PSU issue since they often do this when a cap is going bad or something. But motherboards definitely do it too. Something, a cap or mosfet or something, gets weak, starts getting randomly hot and causing protections to shut down. Then when it cools off, works again for however long.

Both the board and the PSU are somewhat mediocre quality and could easily be the issue. I mean, short of maybe swapping in another PSU if you know somebody with one you can borrow or if you have another, then it's pretty much take your pick and roll the dice on whether it's board or PSU. Generally I like to roll the dice on a better quality PSU because if it's the PSU, then the problem is solved AND you have a nice, new, good quality power supply. And if it's not the problem and you have to get a new motherboard as well, well, you STILL have a nice, new, good quality power supply, which is in fact a good thing since it's going to be more likely to help prolong the life of your new and old hardware. It can certainly go either way though. Or even none of those ways I guess.

I suppose it could even be something like a memory module that's flaking out once it gets warm or a graphics card doing the same. But usually you'll see other signs of problems with those like errors, BSOD problems, driver problems. Usually if it just shuts right down and it's a system that was working fine for a good long while, then it's usually just about got to be board or PSU in that case.