Pc fault detection help.

[Protitan20xx]

pc specs
motherboard - MSI B450 GAMING PLUS MAX Motherboard ATX
CPU - AMD Ryzen 5 2600 Processor
CPU cooler - stock wraith stealth
GPU -XFX Radeon RX 580 GTS XXX Edition OC 8 GB GDDR5 3xDP/HDMI/DVI-D Graphics Card
RAM -HyperX Predator HX432C16PB3K2/16 Memory Module 3200MHz DDR4 CL16 DIMM XMP 16GB Kit (2x8GB)
PSU - Corsair CX550M/CP-9020102-EU ATX 12 V Power Supply Unit
memory - SanDisk SSD PLUS 240 GB Sata III 2.5 Inch Internal SSD
Western Digital WD10EZEX 1 TB PC Hard Drive

brother brought this pc to me because its been having issues however i cant for the life of me figure them out.
full disclosure this pc had artifacting issues as well as sudden power offs that we never got to the bottom of but stopped happening after adjusting some settings and updating driver. this was over a year and a half ago.

now weve got it randomly refusing to turn on with three long beeps which should indicate a memory issue. leaving it unplugged for a few minutes allows us to actually boot but all mem-tests ive run show that the memory is running fine.
ive double checked the VRAM as well through programs and it also seems fine. so im not sure what im missing here.
the fault is not repeatable and happens purely at random ( brother says its happened 3-4 times over the last year)
i unfortunately dont have any extra hardware handy to test anything in a more substantial way.
just wanted to pick your brains a bit on this one.

 

[Protitan20xx]

Is there any kind relation to temperature in those times?
Like PC has cooled completely.
Also has PSU been disconnected from power before those problematic times?

unsure on temperatures as ive been unable to replicate the issues myself. from what my brother has told me the problems are usually preceeded by a game crash of some kind usually minecraft to which he reboots and then the issue happens. ive tried pushing thermals high using msi afterburner with high loads but havent been able to get any sort of issue to show.
PSU wise according to him he just unplugs the extension cord its plugged into at the wall but only after issues otherwise the psu and power systems have pretty much remained plugged in.

 

[Protitan20xx]

Have you checked that the driver and settings remain in place? Windows loves to auto-update everything.

Have you tried running the system with XMP off?

When it crashes playing a game, what happens exactly? Does it freeze completely (no mouse, keyboard, or audio response, hence needing reset?)?

ill have to have a look over it with him to see if any settings are out of place when he comes back over.
as for XMP im not the most tech savy person so im not even sure what that is. if you could explain where id be able to try that id appreciate it.
as for crashes according to him " the game just froze up mouse was still there but wouldnt respond to attempts to close it so i decided to reboot the computer and it just started beeping" ive asked him if he tried CRTL+ALT+DEL to end through task manager but apparently he forgot to try in confusion.

 

[Protitan20xx]

so far so good. nothing changed in the settings as far as we could tell so i disabled XMP ,ran a few stress tests and let him take it home. asked him to keep me up to date if it makes any difference but might be a while given how its only happened 4 times in the last year.