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I have a desktop computer that won't start at all, I had it for years, and now suddenly when I press the power button I get no beeps, no fans spinning, no hard disk spinning. And the amazing thing that it sometimes works when I press the power button and every thing works normally. Sometimes it works after an hour, 10 hours or 10 minutes after I press the power button and this problem happens when electricity goes out and comes back. If I managed to turn the computer and no power outage happened. I am able to keep turning it on. But when the electricity goes off and on. And I press the power button it may turn on after an hour, two, 10 or not at all.

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Sounds like it could be bad capacitors which used to be a common issue: en.wikipedia.org/wiki/Capacitor_plague. Have a look inside the PC to see if any of the capacitors on the motherboard are bulging or leaking. If not then you might want to try a different PSU if you can find one. –  James Jul 9 '12 at 10:38
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Kinda sounds like a bad power supply to me. Or a bad power button. –  Daniel R Hicks Jul 9 '12 at 12:00
    
I had a look and the capacitors look fine, and i tested the PSU with a paper clip and the fan worked. is there a way to test the motherboard some how ? –  Sniffer Jul 9 '12 at 12:12
    
+1 to @DanH , Power Supply could be dying. –  Rhyuk Jul 9 '12 at 12:24
    
try change motherboard OR power-supply hardware. each was crashed, you must change it. –  EmRa228 Jul 9 '12 at 12:42
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2 Answers

I had a similar problem a few years ago. The computer was off and behind a battery backup/surge protector. The power was out for barely a second, but the damage was done. When I attempted to turn on the PC it would not power up and other times it would. One trick I found was to unplug the power cable from the back of the PC, wait 10-30 seconds and then plug the cable back in. Then, the PC would turn on normally. My guess is this allowed for a discharge of power built up in the power supply.

Ultimately, I replaced the PC's power supply and this fixed the issue for me. Hopefully, the cable trick will allow you to get the PC up and running when you need it, until you find the problem and/or get a replacement part.

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i guess i will try to replace the power supply and see what happens, for now the computer has amazingly has turned on and its working great. this is driving me crazy. –  Sniffer Jul 9 '12 at 13:10
    
i tried replacing the power supply but again the same problem. i guess this will drive me crazy eventually. –  Sniffer Jul 10 '12 at 17:22
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I had the same kind of trouble eventually the 4 Pin to Power supply on the motherboard began to fade then eventually burned out. The problem was the motherboard. I replaced that and since then I've had no problems since.

Tip: take time to pull out the 24 Pin power and 4 pin to the motherboard and examine the connections on the motherboard, mine simply could have been a dry joint leading to a power arc earthing the motherboard to blow.

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