I (fairly unusually) switched my PC off overnight, and when I switched it on this morning, the PSU, case and CPU fans spun up for about 1 second before the machine switched itself off. Pressing the power button doesn't switch it back on; I have to either switch it off and on at the PSU or press the reset button on the front of the case, and then press the power button.
The only way I can get the power to stay on for longer than 1 second is by setting the CMOS jumper to clear the CMOS memory; then it stays powered up and a short dull beep can be heard every 2 seconds (it actually sounds like whirrrr-beep, silence, whirrrr-beep, silence, etc), but nothing else happens. When I put the jumper back to the default position, nothing's changed; the machine powers up for 1 second and then switches off before reaching BIOS/POST.
It's an Abit UL8 motherboard. I did the obvious things like taking out the memory and the PCI cards, but this didn't change anything.
Then I took the CPU out. Attempting to power up gave 5 of those whirrrr-beeps, but nothing else happened; fans kept spinning but nothing appeared on screen (I'd put the video card and memory back in by this point, obviously!)
But now that I've put the CPU back in, I'm back to the 1 second problem EVEN IF I SET THE CMOS JUMPER TO CLEAR.
Also, weirdly, if I flick the PSU's power switch on while the CMOS jumper is set to default, all that happens is that the mobo's power light comes on. But if I flick that switch while the CMOS jumper is set to clear, the mobo power light comes on and the CPU fan spins a small amount. What's that about???
And more importantly, what's my problem here - a dead mobo or CPU or something else? What else can I do to troubleshoot this one?
Did you overclocked your CPU?
Looks like your cpu is with problems, normally when they are overclocked this happens one time, but then the motherboard changed to default bios clock and fix itself, but like you said, you reseted cmos and still happening.
Those 5 beeps i think only means there is no CPU connected.
First i would try changing the PSU, maybe this psu is with wrong voltages and may be overheating CPU, if changing the psu did not help, your cpu may be with serious problems, you will need to change CPU or PSU or both
You don't want to power up the system with the cmos jumper in the "clear" position. You can damage some boards doing this. I would suspect the motherboard or power supply is causing your problem, not the cpu, so I wouldn't touch it anymore.