Just like in the title my PC has an issue when it won't turn on. Power button does nothing, fans do not spin, PC is completely dead. First time it happened was when I put it to sleep, sometimes it wouldn't wake up so I just avoided putting it to sleep as a temporary solution that become quite permanent... Simple power off worked well enough but recently it won't start even when I turn it off. If that happens I need to flip the power button on the PSU for a 30 or so seconds then it turn it back on and I can start PC no problems.

From what I read on the Internet people suggest faulty PSU. Is there a way to confirm that? I don't want to buy a new PSU if the old one is still good. It has little over 5 years so it's not exactly new but certainly not too old.

I also had one crash that looked like PSU fault since PC just shut down suddenly but I blamed it on some power drop in the grid at the time.