Morning all,

I have a tower PC here that's been running without issue for ages. However, after doing a normal shutdown, I went to turn it back on and found that the power button did nothing. I switched it off at the wall and tried again, without any luck.

At this point I should explain the normal power-on process: When you switch it on at the wall, nothing happens for about two seconds, then the fans spin up and it presumably does some self-tests. After about ten seconds the fans turn off again and all goes silent. At this point you can press the power button and it'll boot up properly.

What's happening now: Actually, one of two things. Sometimes it goes through the self-test process seemingly as normal, but then once you press the power button nothing happens.

The other thing that sometimes happens (and I can't find any rhyme or reason for it to do one thing over the other) is that it'll actually start booting up when you connect power, rather than just doing the tests. It starts to load the OS, then powers off mid-boot. I've tried a few different drives and can confirm that this occurs regardless of whether it's trying to boot into Windows, Linux or something more esoteric.

I've confirmed that all the fans are working. I've also tried disconnecting everything except the power cable, including disconnecting all internal drives and removing all cards. The symptoms don't change.

Any ideas? I'm suspecting that it could be the power supply, but it'd be good to get a second opinion.

If anything's unclear then let me know :)