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Following a storm last night -- though without lightning or thunder -- my desktop won't start up.

Symptoms:

  • The external power lights and one internal light on the motherboard light up. The three fans spin.
  • The front power on/off button and the reboot button do not work.
  • The power button which is part of the power supply unit does work.
  • The CD player does not eject when the button is pressed, even when power-lights show that the computer is on. However, when the CD's ATA control cable is unplugged, the CD player does eject.
  • None of the beeps indicating failure in the boot process.
  • Nothing at all shows on the monitor, not even the BIOS or other introductory screens.
  • The monitor works, when tested on other computers; I also tested this computer with another monitor, which also shows blank.
  • To check if it is booting up but incapable of video input, I listened for the Ubuntu startup sound -- nothing. I also tried accessing it over Samba and ping -- nothing.
  • So, the power supply unit seems OK. The boot sequence does not get as far as the harddisks or the CD.
  • Edit based on answers: A voltmeter shows that the power supply unit outputs 5V and 12V as it should What should I now do to diagnose or repair it?

Answer following thread with Chris Harrod: The problem is in the motherboard.


Outcome: A professional PC service shop vigorously cleaned the motherboard and replaced the motherboard battery, which, the technician said, was at the heart of the problem.

That did the trick and the computer is fine.

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3 Answers

up vote 3 down vote accepted

These symptoms indicate a failure of the power supply. I had a similar situation.

I do not think it is a bad motherboard or memory because you can't eject a CD rom on boot.

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But the PSU is powering three fans. It is also powering two power lights and the CD light in front and one internal light, on the motherboard. So how could the PSU be the problem? –  Joshua Fox Dec 13 '10 at 20:03
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If you wanted to be sure you could borrow a multimeter and test the voltage. It's possible the 5 volt plugs are working and the 12 volt plugs are fried. I couldn't tell you more, though. –  Chris Harrod Dec 13 '10 at 20:13
3  
Fans and LED lights probably have much higher tolerances for changes in voltage than a motherboard. –  Ryan Thompson Dec 13 '10 at 22:30
    
Thanks, a friend brought over a voltmeter and the internal power supply is putting out both 5V and 12V current. So, the problem is the motherboard. –  Joshua Fox Dec 16 '10 at 6:59
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Even if you heard no thunder or lightning there is a possibility that a current spike came through the power grid and fried something.

Unfortunately (usually) the only way to find out what is broken is to take things out one by one and test it in another computer.

Start with the PSU and work your way inwards.

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Thanks, but I have an integrated Intel motherboard, so it is not practical to replace it as part of a test: I am not sure I have the skills and in any case, I don't have another motherboard. Is there another way to approach this? –  Joshua Fox Dec 13 '10 at 19:03
    
@Joshua - I'm afraid it's the only way I know. If you don't feel confident doing it yourself you'll have to ask someone else. If you do, either remove the hard-drive first, or ask to sit in when they do the repairs either way your personal data is safe (and if you sit in you might learn something) –  Nifle Dec 13 '10 at 19:30
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I have seen similar behavior caused by faulty RAM. If you have multiple memory modules installed, try each of them by itself, with all others removed. If you have another computer with the same kind of RAM, you can try swapping.

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Thank you. I tried turning it on with one of the two modules removed; then the other one; then neither -- same behavior. –  Joshua Fox Dec 13 '10 at 19:16
    
@Joshua - If you get the same behavior with no RAM, the motherboard isn't doing it's job properly. It should beep at you if there's no RAM. However, that doesn't necessarily mean it's bad. It could still be that the power supply is not providing enough power to the motherboard. –  Joel Coehoorn Dec 13 '10 at 19:57
    
Right, no beep. And the PSU is powering three fans, and turning on two power lights in front and one internal, on the motherboard. –  Joshua Fox Dec 13 '10 at 20:02
    
The fans and lights don't necessarily indicate anything. They are probably tolerant of insufficient voltage, whereas the computer chips themselves are not. –  Ryan Thompson Jan 7 '11 at 20:19
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