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For about a week, my desktop has been acting weirdly.

  • Sometimes, after pressing the power button, it turns on instantly.

  • Sometimes it does not react at all. No sounds, no lights, nothing beyond the click of the power button. (The button's okay, I can test that much.) Disconnecting the power completely for several minutes sort of helps.

  • Sometimes it does nothing for maybe a minute, then suddenly springs into life just when I'm about to walk away. Again, in the meantime it remains completely dead.

This happens regardless of whether the computer was connected to the power source right now, or had been connected for the entire night... It's just random from what I can see.

The PSU appears to be working, though: the motherboard light is on, as well as the Ethernet lights. Unfortunately, I don't have a second compatible PSU to test with... Is it time for a replacement, though?


What makes this more interesting is that the exact same behavior has been reported to happen with several computers at a nearby school in the city.


Any ideas what could be causing this?

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When you say "wheter the computer was connected to the power source... of had been connected for the entire night...", you mean the power cord being connected or not to the wall socket ? –  woliveirajr Mar 26 '12 at 20:42
    
@woliveirajr: Yes, that's what I was trying to say. –  grawity Mar 26 '12 at 20:47
    
and when it's on, does it stops or turn off? If it's working, if you move it, shake it (just a bit), etc, makes it goes off ? –  woliveirajr Mar 26 '12 at 20:50
    
@woliveirajr: Once it turns on, it keeps working just fine until I request Windows to power off. (Both "Shut down" and "Hibernate" have the same results above, but it always wakes up normally from "Stand by".) Moving the computer does nothing. –  grawity Mar 26 '12 at 20:52
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3 Answers

Edit: the original answer is left below.

You provided two valuable informations in the comments: your computer have problems to turn on, but once it's on, it works ok. When shut down with "power off" or "hibernate" (both of them really turn off the computer), it might have the problems to turn on. When left in "stand by" (which means "on, but use as little energy as possible), it keeps ok.

And it doesn't seem to be bad contact in the power cable.

Try another test: under high load (like playing video, copying files, reading dvd) at the same time, does it keep working? Power supply with problems would turn off when highly demanded.

--> in general, this kind of problem ("doesn't work, only after few minutes") are related to heating of some component giving trouble, or a capacitor failure in some circuit. In general, in the power source.


Let's consider that all the eletric things in your house are ok: no problems with TV, etc, and you're sure that you can get 127 volts from the wall socket.

You could have a problem in the wall socket; You could have a problem in the plug of the power cord (either in the wall, or in the back of the computer); If you have some no-break, etc, between the computer and the wall socket, could be that equipament too; Then the power supply of your computer; and, finally, the motherboard.

You also said that the power button is ok. Since a long time ago, this button can be "by-passed" by shortening the two pins in the motherboard, the pins that they're connected to. Try that to make sure the problem isn't, really, in the button.

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I think we can isolate this to one of three things:

Motherboard Power button/Case Power unit.

For Power unit, possibly try and switch with another known good one - but you have already said it is working...

If the local school has been having the same issues, it could identify bad power in the area. If this is the case, you may want to consider buying a UPS.

To test the button issue - try looking at where the power button is connected to the mother board and using a pen/metal tip to power on - if this doesn't work, it could identify the motherboard is failing...

... Quite frankly, if there was a component failure, you should at least get lights/fans e.t.c. so, I think at this point, if the power unit is good, and it doesn't turn on through completing the jumpers, I think it means the board is failing.

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If you know the button is okay, and you have heard of similar problems, it may be a virus. I would do a deep scan using at least 2 different anti-virus programs.

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