Computer shutting down and starting up by itself
 

I have a weird problem. One of my PCs sometimes won't start when I press the button (there is power to the motherboard; I can see the little green light on it) but then after a few minutes it springs to life. Other times, it will start but then stop by itself, then restart some time later. I don't think it's temperature-related.

I'm thinking power supply or motherboard, maybe RAM, but before I start on a "change this change that" maintenance task (can't even MEL this one!) I would be grateful for any ideas from the floor.

Thanks!

It might be worth leaving it unplugged for a bit then unplugging and replugging everything in again such as memory, power cables, cards etc

Is there any numbers shown on the motherboard or coloured lights as they often refer to the fault, you can normally get the code reader on the cards manufacturers website.

Fast guessing:

Power Suppy, it's also one of the cheaper parts.
Maybe the Windows Tool "Event Viewer" gives a hint (but unlikely). Check Computer Time roughly in sync with your clock. Note time of next shutdown. Thereafter, open Event Viewer and search if a hardware component is suspicious.

Thanks all, it was the power supply. Fortunately (and by chance) I could replicate the shutdown by plugging in my wifi dongle. There was a muffled click when the machine died each time, and the power button wouldn't respond for a restart unless I disconnected and reconnected the power lead.

I once replace the electrolytics around the CPU because of uninvited restarts. It wasn't the easiest of jobs.

Yikes! Definitely a "Repair by Replacement" job, that one!

Yes, and I wanted to over-spec the capacitors. As a result, they were about 10% larger in diameter. I could do this by leaving the wires longer and shoving the c's over here and there. It worked for years.

Got the clue from someone on here.

The increasingly common 'bulging' capacitor issue?

I've just replaced a couple of electrolytics in my bathroom extractor fan to fix erratic behaviour as it neared the end of the timer interval. I've also fixed a computer monitor that way when it became difficult to turn on and off.

At least it's easy to see where the problem is.