I was on my PC today for most of the day and then all of a sudden it switched off. It didn't showdown or anything just turned off and then I couldn't get it to turn on. I noticed that there was a quiet high pitched buzz coming from inside the PSU. I checked all the cables to see if anything was loose but this wasn't the case, I powered off at the socket then back on and tried to reboot but no joy. The power and reset buttons on the mobo are on and lit so power is getting to them. There are no beep at all from the mobo warning speaker. Can anyone advise?
You can unplug your PSU from the wall, wait about an hour (with it unplugged). Plug it back in and try again. If that works, chances are good that your PSU is dying and you'll want to replace it.
What model PSU (or computer if prebuilt)?
Sounds like a dead PSU, your Motherboard still has the LED's but no power is being delivered to the main components. You can double check, jump start the PSU with a paper clip (check on google), if the fan doesn't spin it's probably dead or dying.
I just checked this out and tried to jump it with a paper clip but no good. It's only 6 months old and was fairly expensive but from a local company in England. I voided the warranty because I opened it to try and fix it. I think I will go with a better brand this time.