The main household pc has died. For a while the fan was making a buzzing noise and we were going to replace it either with a heatsink or with a new fan. A couple of days ago, my g/f turned it on and it went on and then off.

If we just leave it plugged into the mains, the LED on the motherboard comes on. As soon as we push in the power button, it all turns off.

Mothing has been added or removed from the pc. I have also tried unplugging all peripherals and then powering on - no change, no power.

I suspect it is a power unit problem, but before I go out and spend money on parts which may or may not be necessary, does anyone have any ideas as to what could be the problem and any steps I might take to resolve them?

Thanks in advance.

one of the first things i try when troubleshooting is taking all the hardware out of the box and only leaving ram, video, for i can see if it is a hardware issue (ex. sound, nic, etc) ..
then i will cut down on the ram (if there is more than one stick) and if it still dont' work then try another stick etc... then if you can try a different power supply from another machine (still without all the hardware) and if possible after trying a known good power supply, try changing the cpu, and if that still fails then if nothing is working, maybe with bare bones, put a different video card in (again if you have a spare known good one, and with the known good power supply) and if none of that works, then i would suspect a board issue ... look for burn marks, melted/leaking capictors, etc ...

Since you mentioned your fan was making a noise, newer motherboards have fan sensors when you press the power button, if the BIOS does not sense any fan speed it will shutdown. This feature can be disabled.

DrOzz and MichaelK

Thanks for this info. It does look as though the fan is at fault - I have tried powering on with no extras and it still fails. The fan was sounding as though the bearings were at fault, it also didn't seem to be cooling the system as well as it should. I'll grab either a good heatsink or a bigger fan and see if that solves the problem.

Thanks again.