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everybody. I just built my own computer. This is the second time that I have done so, but last time I did so with a friend that was more knowledgeable than I am. The computer is built and everything appears to be plugged in, but when I hit the power button, the computer begins to turn on and shuts off almost instantly, then "flickers" on and off.

The fans and case lights will flash for an instant, then everything shuts down. Two to three seconds later, they will flash on again for a second or so, then back off, and so on, until I kill the power. I'm guessing that this is the fault of the power supply, perhaps due to some signal from the motherboard, but I'm not sure what is going on.

Does anybody know what sort of misconfiguration could cause this sort of thing?

My thanks.


Problem persists when booting using only Mobo, CPU+Fan, PSU, and single stick of RAM. It is likely not the RAM, as I have tried with multiple different sticks of RAM. That leaves Mobo, CPU+Fan, and PSU.

I'm guessing that the PSU or Mobo is faulty. Is there any way to identify which one, and/or is there any connection that could be messed up between the PSU and the Mobo/CPU that could be causing this behavior (on for an instant, off for five seconds, on for an instant, etc.)?

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up vote 3 down vote accepted

This could happen if your processor fan is misaligned, or if your ram is not plugged in well or you have a faulty power supply. I would like to suggest a few steps:

  1. Confirm that you have plan the fan above the processor correctly, the processor could be overheating due to misalignment, this is a very common mistake with folks who have just begun assembling computers.

  2. Check whether you have plugged in your ram correctly, try pulling it out without letting the side notches loose

  3. Start-up the computer with bare bones to find out where the trouble lies, do not plug in anything not necessary initially, i.e. just check if you are getting display. Keep only your power supply [obviously! ;) ], motherboard, processor and processor fan, monitor cable (VGA, DVI, HDMI whatever you are using) and ram connected to the board. Also if you have a graphics card DO NOT connect it initially, unless you don't have an onboard connector. If you have to use a graphics card, check if its plugged in securely.

  4. If your computer doesn't act up the way it does after the 3rd step, then try to plug in your hard-disk and check what happens.

Kindly write back what happens after these initial checks, so that we know that the hardware has been placed correctly on the board. If you still face any problems after these steps we can take it further from there.

The main problem with people new to hardware is that there is a huge possibility that parts are not been plugged in well to the motherboard, not doubting your computer assembling skills here but its best to be sure first, than sorry later.

Some further reading for common reasons on why a computer could possibly keep restarting/rebooting itself.

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Yeah, I'm hoping that I just mis-plugged something in. I don't think that it's a POST issue, as the mobo does not beep. I tried booting up with only mobo, CPU+fan, PSU, one stick of RAM, and GPU (there's no onboard video), still the same issue. The weird thing is that while it only stays on for an instant, every four to five seconds it comes on for another instant then cuts out again. Any idea what could be causing that? Thanks. – So8res Jul 31 '10 at 21:29
Is the hardware that you are using to build this machine new? or are you using them from older machines? You will have to check the working condition of the older parts. – rzlines Jul 31 '10 at 21:34
Also just tug on all the hardware that you have plugged in, that way you can find out if something is not properly plugged in. – rzlines Jul 31 '10 at 21:35
If all the hardware is in correctly, then this mostly happens if your RAM or Graphics Card is faulty – rzlines Jul 31 '10 at 21:37
put the packaging material you got from your mobo etc on the table or whatever surface you are working on and then place the mobo on it. Make sure the packaging material in placed as flat as possible. – rzlines Jul 31 '10 at 21:50

Motherboards have a feature called P.O.S.T., or Power On Self Test. If something isn't hooked up or plugged in right, this is how it tries to tell you. Depending on the motherboard, it'll use a series of beeps or a couple of leds.

Use this guide to diagnose the problem.

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I'm not sure it's a POST failure, I just noticed that if I don't immediately cut the power, it will come back on for an instant every three to four seconds. Is that the behavior that you would expect with a POST failure? – So8res Jul 31 '10 at 20:44
When you hear beeps or see a series of leds freaking out, you can consult your motherboard manual to find out what POST is trying to tell you. If it doesn't even come to that, like in your case, there are some other things you can try. The article I linked names some, like making sure all fans are spinning properly, or seeing if the machine stays on if only the necessary stuff is plugged in. – Kenny Rasschaert Jul 31 '10 at 21:04
To continue on the last thing I said: Try it with only the cpu, cpu fan and a stick of ram, see if the machine stays on at least. If it does, you can add parts from there. If it doesn't, it's possible that the power supply or motherboard is faulty. – Kenny Rasschaert Jul 31 '10 at 21:13

Is it safe to assume that my power supply has an issue?

More data:

When I press the power button, everything comes on for about half a second then goes dead for about five seconds, then comes on for half a second, and so on and so forth, until I cut the power.

I tried booting with only the bare essentials, the problem persisted.

I tried switching between multiple sticks of (new) RAM, the problem persisted.

I took the mobo out, placed it on the anti-static packaging, and tried again, the problem persisted.

At this point, can I safely assume that the PSU is the issue and send it back? I don't want to wait a week and figure out that that wasn't the issue.

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it could also be a mobo issue – rzlines Jul 31 '10 at 22:54
do you have a spare psu or could you borrow it just for testing purposes? – rzlines Jul 31 '10 at 22:55

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