Odd one: turn the pc off at the mains and leave it for a while. When I turn the mains back on the computer will not power up. However, if I leave it for 15-30 mins it starts up normally. Anyone know what might be causing this?

How far does it get? Is it completely dead? No lights noise etc?

Power supply could be on its way out.

Nothing at all initially.

Why does it start up after a while if the power supply is dying?

Press and hold the power button for 10 seconds whilst said computer is turned off at the wall. Turn the power back on and hit the power button again.

Worth a try.

Once it's started,does it run okay,or cut out?
Ian

I've had the pc on for a while now so I will have to leave it for a bit to test. What does the button pressing do?

Would agree on the PSU/Switching issue

Once it's started,does it run okay,or cut out?

Once it's running it runs without a problem; shuts down and starts up fine. It's only when it's unplugged for a while that it doesn't work for a bit.

Pressing and holding the power button doesn't do anything. Anything else it could be?

A lack of PC knowledge and how to set your Power Options.

Try tweaking it's nipples.

Any helpful suggestions? 🙄

Could be the CMOS battery.

JonW – Member

Any helpful suggestions?

Any helpful information as to machine, OS, Power options setting ?

I've already changed CMOS battery thinking it was that but it made no difference.

PC is home assembled from ASUS bare bones about 5 years old. Running win7 with default power options.

There's a 'power ok' line that comes out of the psu which the motherboard checks before starting up. The psu could be on the way out hence sometimes it isn't 'ok'. PSU's are the most unreliable bit of a pc in my experiance (had one fail over christmas), but cheap and quick to fix.

Aye worth checking cables, cooler, ram and video card are all nice and snug.