Question Pc doesn't turn on sometimes, sometimes it runs fine

[Sayan_Deep]

So my friend is having a pretty weird problem. Sometimes his pc doesn't turn on. When turning the power on from wall, the lights on the motherboard turns on. But hitting the power button does nothing. No fan start up in neither mb nor the psu. This issue started suddenly. Pc worked fine for about 2 years. Sorting the power pins doesn't work either. But sometimes it starts just fine. It's not an issue of the cabinet cause sorting the power pins doesn't work when it refuses to start. So, replaced the psu with a known working psu and it still didn't work. Same issue persists. Sometimes it starts. Sometimes it doesn't.
Checked the original psu by sorting the green & black wires. It turns on.

Specs:
cpu-Ryzen 2200g
Mb-asus prime a320m-k am4
Ram- 8gb ddr4 3000mhz
Psu-some generic 450w psu that came with the cabinet (he had plans to replace it)

Replugging everything didn't help. I think it might be a motherboard issue. But don't have any replacement to test it out. My friend decided to show a technician but the damn pc decided to start up everytime the guy tested. But as soon as he left it's back doing the same thing. Should I call an exorcist?
All the components except case & psu are under warranty. So should he go for RMA? If so, which one might be the culprit? I'm not even sure if it's the mb in the first place. What should I do?

 

[Greeko85]

Might be a silly question but when the pc isn't starting up are you plugging the pc on the same wall socket each time or is there a multi adaptor used somewhere?

 

[Sayan_Deep]

Might be a silly question but when the pc isn't starting up are you plugging the pc on the same wall socket each time or is there a multi adaptor used somewhere?

There's no additional adaptor or anything is used. It was tested on different wall sockets and also in different houses. Same thing happens.

 

[Greeko85]

Have you tried resetting CMOS or even changing the battery? Always worth a try

 

[Sayan_Deep]

Have you tried resetting CMOS or even changing the battery? Always worth a try

Tried resetting cmos multiple times. Didn't change the battery though. Outcome was the same. No certainty whether it'll turn on or not.