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Whenever I shut down my computer, or put it in sleep/hybernate, it turns on after two seconds. It doesn't post, it just powers on and then idles. To actually turn it off, I switch off the psu. The problem is now, whenever I switch the psu on and try to boot, it doesn't always turn on. It takes a good amount of flicking the psu switch on and off before the motherboard lights up.

So far I've determined the things its not:

  • its not caused by the mouse or network waking up the computer. I've been able to go into hybernate for the past year. And all "wake on X" settings in the bios are diabled.
  • its not a scheduled task waking up the computer at a given hour, it occurs every single time
  • its not due to an upgrade or new installation, since I haven't done either in a very long time

I'm sure its a hardware issue. So I'd like to know, is my psu dead, or the motherboard? The psu is an Antec Earthwatts 600w, the motherboard is an Asus P5Q-E, both one year old.

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I have a similar problem with a Gigabyte motherboard and Antec Earthwatts 500 PSU. Mine will sleep/hibernate, but if I shut it down it will sit there with the fans still running for a couple of minutes and then boot up again. I deal with it by just putting it to sleep after it boots up again. I also noticed that if I power it off with the switch after it thinks it's off, on next boot sometimes my mirror will want to rebuild. It's gotta be something in the BIOS. –  Bratch May 4 '10 at 14:59
    
Check my answer, your motherboard might be on its last legs –  Patrick May 24 '10 at 5:13

3 Answers 3

up vote 1 down vote accepted

This turned out to be two problems.

The problem is now, whenever I switch the psu on and try to boot, it doesn't always turn on. It takes a good amount of flicking the psu switch on and off before the motherboard lights up.

As quack pointed out, the PSU was a likely candidate. It was clearly dying, so I replaced it. Now the power always turned on. However, the following problem remained:

Whenever I shut down my computer, or put it in sleep/hybernate, it turns on after two seconds. It doesn't post, it just powers on and then idles.

While attempting to solve this, I went about the following:

  1. Cleared the BIOS many, many times
  2. Tried all possible permutations of bios options relating to power and sleep
  3. Systematically removing hardware/peripherals and then booting/sleeping, until I ended up with only motherboard, cpu, psu, one stick of ram, and a power cord connected (I scheduled a task that put the computer to sleep one minute after boot to test)
  4. Investigated the event viewer for problems
  5. ran powercfg -LASTWAKE to get a report on what woke up the computer

This led me to replace the motherboard. Now I have no problems either booting or sleeping. So in conclusion, the replacement of both the PSU and the motherboard solved the problem.

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Try clearing the BIOS by completely removing power and using the CMOS jumper. Then take BIOS default settings and go into ACPI and turn off any S2/S3 sleep or hibernate modes. Look for and turn off any settings about what devices can wake up the machine, particularly network.

If that doesn't work also check try toggling any BIOS settings about legacy versus USB keyboards and mice.

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While it could be either, the PSU is the more likely candidate, and probably easier/cheaper to replace. Try swapping the PSU out for a known-good (or "new", that works too) PSU of equal or greater wattage.

If your problems disappear, blame the PSU and move on.

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Ended up replacing the PSU since it flat out refused to turn on any more. Now the new PSU seems to turn on each time, but the computer will still turn itself on after sleep/shut down. Also, the delay with the old PSU from off -> on was 2 seconds, now its 5 with this one. –  Patrick Dec 11 '09 at 2:42

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