System Won't Stay On Unless Power Button Stays Depressed

[Nathan D.]

First off, if someone feels this is in the wrong category/sub-category, please move the thread and accept my apologies. Because I am leading towards this issue being caused by the motherboard, that's why I posted it here.

I have had my custom built PC for over 2 years now. Everything has been great until recently. My system one day just cut off out of the blue; I'm on a UPS so I knew power wasn't the problem. I tried to turn it back on and it came on and posted as normal but after about 10 seconds of power, it turns off again. Because I am surprised by the symptoms, I don't do anything and just try to think of what happened; during this thought process, the PC turns itself back on and then back off again. I noticed that it would continue to turn itself on and off repeatedly and apparently indefinitely.

If the power supply switch is turned off and then turned back on, the system will not turn itself back on again unless the power button is depressed. I noticed that if I press the power button, the PC comes on, and then I press the power button again and leave it depressed, the system stays on until the power button is again released. I have been running my PC for a couple months now with the power button taped down so that the PC turns on. The PC runs great and has no limitations at all with the power button taped down.

As far as troubleshooting, I confirmed it is not the case power button that is the issue as I removed the motherboard from the case and used the power button built onto my board. By removing the motherboard from the case, this also confirms that a short is not the cause.

My only two conclusions; the motherboard is bad or the PSU. I am more inclined to think it is the motherboard because if the PSU was not putting out it's rated capacity, the PC would have other signs of problems especially when playing games or other resource intensive tasks that would draw more power from the PSU.

Please advise. Any input will be appreciated. Thanks in advance!

PS: If you feel the specifics of my hardware are necessary to help form your opinion, I'll be glad to post. Keep in mind, the system has been fine for 2 years and has always been behind a UPS.

 

[rainless]

Sounds like you have the power plug from the case to the motherboard plugged in backwards.

 

[trents]

Sounds like you have the power plug from the case to the motherboard plugged in backwards.

If you mean the case's front panel power lead connector coming from the power button then I don't think it matters which way you flip it. It's just something that completes a circuit and does not depend on polarity.

Nathan, you have a power button built onto the motherboard? What makes you think that eliminates the case's power button as the problem? Seems to me what you have done is eliminate the motherboard as the problem which leaves either the PSU or the case power button as the culprit. Do you have access to another case that you could remove the front bezel from so as to try another power switch? That would help you discover whether or not that is the problem or the psu. I always keep a spare power button around for testing motherboards out of the case. I removed it from an old case that I disposed of. But you can buy them for not much too: http://yhst-28478524343892.stores.yahoo.net/con-6310.html

The problem could also be the ATX power on subsystem of your power supply which would not affect its operation under load. The rest of the psu could be fine. But I would try another power switch first. Start with the things that are easy and cheap and go from there.

 

[Nathan D.]

I eliminated the power button from the case as being the problem as I removed the motherboard completely from the case (including removing the button power button wires from the motherboard to the case). The motherboard literally has a power button built onto it for testing purposes. Also, instead of even using that power button built directly on the board, I simply shorted out the two pins for power on the board with a screw driver but the issue remained.

I will definitely try a different PSU if you still feel that could be a possibility after reading the above.

 

[trents]

Yeah, try a different psu if you have access to one. Or, you might conside buying an inexpensive one for testing purposes and just keeping it around for a backup. i've been building systems for some years now and believe me, it always pays to have extras of this and that around for testing purposes or to fill in the gap when something goes belly up.

Where in VA do you live? That's my home state.

 

[QuietIce]

So let me get this straight. You shorted the board power pins to get the unit to come on but it shut back off again?

Is/was the PSU clean - no build-up or heat issues there?

Just for grins you might try unplugging everything from the PSU but plug in all the fans you can get your hands on. Then connect PSU pins 3 & 4 (green & black). The PSU should stay on as long as the pins are connected ...

 

[repilce]

sounds like a faulty board to me.
pretty simple really..

just use a piece of wire or a two pin header for a switch and tie them together.. if system fires up and runs right as long as they remained touched and everything is in spec.. faulty board...

but i'm no expert.. and have seen weirder things happen.. so if u got a spare psu just laying around.. eh why not