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System power issue - PC not powering off

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December 28, 2010 4:48:46 AM

Having a strange issue with a system I've been working with for almost a year. Recently I hooked up my system to a HDTV to play some movies and somehow since then my system is unable to power off. I go through the normal process of shutting down and it's clear that the OS is shut down, my screen goes blank, however the system doesn't power down itself. Holding the power button doesn't do anything either, and ends up restarting the system. The only way i've been able to power off my system is by using the on/off key on the back of the power supply itself! What's weirder is that once I've turned off my system, to turn it back on all I have to do is flick the PSU on from the back and the system regains power, however does not boot. I need to press the 'power' button on the front panel for the system to boot up BIOS and start working. Other than this my system is working just fine. Not sure what the source of the problem is, however I've checked the power and reset button attachments to the Mobo and they're correct, I've also tried switching them (just in case the power button was somehow stuck) and there's no difference. I've cleared CMOS, took out the motherboard battery and updated BIOS and nothing worked! Any help is really appreciated...

My system
Asus p7p55D mobo
GEIL 2x2GB DDR3 Ram
intel core i5
ato 4850 512MB
OCZ fatality 550W PSU
3 HDD


* this system has been working for almost a year and nothing was changed from the time since it was working properly to the time it was hooked up the to TV and these issues started occuring*
a b B Homebuilt system
December 30, 2010 3:22:40 PM

Check the power management settings in the BIOS - look for it. Note it down, and see if setting the BIOS to defaults changes that setting. Not sure if something changed the power on behavior.

Also check the power settings in Windows. Set to default.

Looks like the motherboard is on its way out for RMA if this does not work.
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December 31, 2010 3:37:23 AM

I've checked all sorts of windows and BIOS settings and have found nothing that works! Could it be an issue with the psu?
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a c 113 B Homebuilt system
December 31, 2010 3:49:48 AM

That's possible. If it were it would simply start on it's own when unplugged from the board. Unplug from the wall, then unplug from the board (both power connections, 24-pin and 4/8-pin). Then plug the PSU back into the wall. If it's running on it's own you have the culprit.

Beyond that your board could have a short, for instance from a dropped screw.

Or a bad board as pinaklonar suggests.
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a b B Homebuilt system
December 31, 2010 3:53:06 AM

+1 ^
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December 31, 2010 3:56:46 AM

Thanks for the replies, I will definitely check out the PSU and look for any loose screws that could short the board. Is it likely that a board goes bad just like that while it's been working for a year?
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a c 113 B Homebuilt system
December 31, 2010 3:59:17 AM

Well, define likely.... after a year probably not very. Boards fail right away or after several years, but could go at any point.
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a b B Homebuilt system
December 31, 2010 9:36:17 AM

I'd say it's very unlikely that the board or PSU just *happened* to fail at the exact same time you made another change. Look at everything involved with the HDTV hookup first.

What this sounds like to me is that there's a "wakeup" setting in the BIOS that's enabled, causing your machine to turn right back on as soon as you turn it off, based on some external cue (which the HDTV is probably providing). There are usually a handful of obscure settings like "Wake on PME," "Wake on LAN," and so forth that will cause your machine to power on for no apparent reason. What they do is basically tell your system to turn on anytime there's incoming data from a particular device or port.

I once had a machine that did exactly the same thing and drove me up the wall, until I figured out that enabling "Wake on PME" meant that every time my router tried to contact my system (which was constantly, since that's a part of routine operation) it would cause the machine to power on because it was getting pinged through the Ethernet port. It would only stay off when I turned off the power strip, after which I could turn the power strip back on and it wouldn't boot on its own until I told it to. The fact that your machine doesn't turn back on from a brute-force shutdown on the PSU would seem to confirm a similar kind of problem.

I would imagine that connecting to your TV through an HDMI cable could have the same effect if the TV is constantly sending out HDMI handshake attempts or something of that nature.

Anyway ... look through the BIOS for those settings and see if it helps. Resetting the BIOS to defaults might not do the trick, since often times the factory settings have "Wake on PME," etc. enabled.

If you have trouble with this, one surefire way to test this theory is to unplug your computer from the TV and Ethernet, try to shut it down, and then see if the problem still occurs. If it doesn't restart, it's almost certainly a BIOS problem. If it still restarts, then you start looking at hardware.
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December 31, 2010 7:29:29 PM

^ the HDTV is not being used, this problem continued even when I went back to using my usual monitor.

I tested the psu alone, and what seems to happen is when the psu is completely unplugged from everything on the PC it still runs when I flick button on the psu itself. I'm not sure but I would think that's normal behavior, but again I could be wrong.

Another thing to note: I tried to troubleshoot the system to see if a component was causing the problem. I started out with just the mobo, CPU and one stick of ram. The system still had the same issue. I took it a step further and removed the ram stick to see if i'd get an error beep from the mobo. Strangely enough, there was no error beep when the system automatically turned on BUT I did get the error beep from the mobo after I pressed the power button while the system was already 'on'. What do you think?
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a c 113 B Homebuilt system
December 31, 2010 10:22:04 PM

There you have it. If your PSU fan is spinning when it's not connected to anything that is NOT right. The green wire on the 24-pin connector is supposed to be shorted for the PSU to actually run. The only power that the PSU should supply when it is not shorted is the +5VSB (used by the computer in sleep mode).
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a b B Homebuilt system
January 1, 2011 9:36:47 PM

^ Second that. The PSU is not supposed to be spinning on its own.
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January 8, 2011 11:16:52 PM

Best answer selected by vancoRx.
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February 23, 2012 1:29:58 AM

This topic has been closed by Mousemonkey
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