Make sure the clear cmos jumper is in the correct position 😀 and the FSB jumpers are set to the correct settings and you are using compatible RAM and CPU. Other than that I really cant think of anything else.

Left out in the rain? Ouch... I would inspect the board first, search for leaking or bulging capacitors and burn spots/fuses.

Afaik if the cpu fan doesn't spin then it's a cpu problem,can u try with another cpu?

A bad CPU or RAM shouldn't keep the board from turning on, unless those parts are electrically shorted. The Clear CMOS jumper could have this effect though. I've read (but not experienced) that some later boards won't turn on without a CPU, but I've never seen that behavior on a socket-A Athlon board.
Does the fan twitch at all? Does the LED go out after you hit the switch? If these things are happening, then there could be a short that's causing the PSU to turn itself off due to overload. If there's a short, you might be able to find evidence of it with a multimeter at the ATX connector.

It's possible the fan header is dead. Have you tried all of them? Even then, it's possible all of them are dead (depending on the design, they could all die at once).

You could try cleaning it, just in case there's some debris somewhere that's causing the problem. If it was outside then that's possible. Probably won't help though.

I've run into some motherboards that don't appear to be shorted but just won't switch on. I don't think I had any luck figuring them out. There was one that I forced to run by jumpering the appropriate wires underneath the ATX power connector. It ran that way, but eventually it stopped POSTing. I guess there's a reason it didn't want to turn on and forcing it to run may have killed it. Still, if you get to the point of throwing it away, I guess you could try that as a last ditch thing. Depending what's wrong, be ready for a bang. The PSU *should* protect itself, but just in case it doesn't, I'd only try that with a PSU you don't care much about.

Nahkri wrote:

Afaik if the cpu fan doesn't spin then it's a cpu problem

shamino wrote:

It's possible the fan header is dead.

To be clear, I am referring to the power supply fan, not the CPU fan. That is: the power-switch pins on the motherboard produce no response from the power supply. (And it seems unlikely that the fan would be dead in each of the three PSUs I tested.) But it's weird that the LED on the motherboard still switches on, isn't it?

I guess looking at the Clear RAM jumper is worth a try.

Maybe I should dump it on eBay if all else fails; I've managed to sell dead boards there before. (Properly described, of course.)

The LED from the motherboard is probably directly hooked to the -5VSB line through a resistor, so even if the entire mobo is busted that LED may light up, since the PSU provides that line regardless of what the motherboard is doing.

If the motherboard battery is removable, remove it and all power (even standby) to the motherboard for awhile. Try the clear CMOS jumper if there is one. Insert fresh battery (or apply power without battery). It is possible that battery is low enough to stop RTC oscillator from ticking but not low enough to reset operation. If it does not tick, one motherboard I have stops responding to power button. I managed stop it by touching with oscilloscope probe, but moisture from rain could have stopped it too.

I had such troubles with a jumper on RESET pins. I wanted to put it on turbo, but for some reason I put it on the wrong side of the header. Took me several hours to find out why my computer died all of a sudden.

Well, I did suddenly realize that the button I thought was the power button was actually probably the reset button. (It's a weird-looking case.) Not that pressing the correct button helps much.

I tried taking the battery out for a couple of hours and nothing has changed. One thing I did notice is that after disconnecting the power cord from the power supply, for a brief instant when the LED goes off, the CPU fan will spin – which does lend some support to the "overvoltage protection" idea.

The motherboard manual suggests there's a "keyboard power" jumper; maybe that's worth a try.

Well just double check from the manual what pins are power switch pins and use something that is known to work as a switch there (jumper, screwdriver, button from another case...) as paper clips could have oxidation and oily fingerprints on them so they may not take contact so well.

If that fails, use the paper clip directly on ATX connector to force the power supply on. Connect the green PSU_ON wire to black GND wire. Stand back in case of fireworks.

So the only thing I did was move the "Keyboard Power" jumper, and of course I plugged in a PS/2 keyboard. Mashing the keys wasn't doing anything, but then I tried the power button again and it inexplicably sprang to life! How utterly incomprehensible! Some kind of built-up static charge, I guess?

I suppose that's one trick I'll have to remember next time I encounter a similar situation. Now I have to decide if I can justify keeping this thing around.