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I was using my computer when suddenly it shut down. It was assembled 7 months ago, while the PSU is two weeks old, though it is not a good brand. When I try to reboot it, a led on the case fan lights up for a split second and then turns off. Nothing else moves or seems working. I tried removing and connecting again the connectors to the motherboard, I tried to unplug it for a half minute, but nothing seems to work. Could it be the PSU?

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I also tried to change the power cord, but nothing changed, red light on for a split second and no other sign of life. –  Elena Dec 19 '12 at 23:12
    
if nothing has been added lately, I would unplug all external usb devices... mice/keyboard/camera/exthdd etc... and then try starting it. Then I would unplug any internal cdr/dvd or hds not needed to boot... even pci cards –  Logman Dec 19 '12 at 23:35
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"it is not a good brand" "nothing seems to work" "Could it be the PSU?" Absolutely. This behavior is usually a power supply, or less likely the motherboard. (In theory lots of other components could cause shorts or grounds that would cause this behavior but it's really unlikely.) –  Shinrai Dec 19 '12 at 23:40
    
It shouldn't be too hard to find someone else with a compatible PSU. Try that and you can rule your PSU in/out –  Lee Taylor Dec 20 '12 at 0:23
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4 Answers 4

After trying everything else..,

Without knowing much about your power supply and your technical depth; seems you are able to remove the PSU. You can either order a new one online or take this to a shop that might be able to test it.

Often they have an internal fuse that can be replaced inside, but in some cases maybe not.

Even if it was your MB or some other part, the fan on the PSU should still work and supply power.

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Perhaps the PSU has been overloaded by all of the components inside the computer (this could happen if you get a PSU that too few watts for what you are trying to power)? Here's how to troubleshoot this:

I would suggest unplugging all of the components (optical drive, hard drive, etc) from the power supply. With only the motherboard plugged into the power supply, try turning the computer on. If it stays on, then that will tell you there's a problem with either the amount of components you are running, or a problem with one of the individual components.

If the power supply still doesn't turn on with just the motherboard, try unplugging the motherboard. There's a way to power up a PSU without the motherboard connected (you can see that here: http://gideontech.com/content/articles/196/1 ). If the PSU still doesn't stay on, then you obviously have a bad PSU. If it does stay on, either the MB or the PSU is bad.

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It is possible that there is something shorting out the motherboard. You said that you recently assembled it. Have you moved the computer since then? Check to see if there are any loose screws inside the case. I've see this behavior come about due to a screw getting lost in the case and shorting a couple pins on the motherboard.

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Clear CMOS. remove all unnecessary hardware such as HDD, sound card, external hardware except monitor.

Try only one RAM-stick, try it in another slot, change ram-stick.

connect a wire from green to ANY black in the large 24/20-pin ATX-cable. given that power is supplied to it, it should start up.

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