Troubleshooting new computer: shuts down instantly

Question

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.

EDIT:

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.)?

Answer 1

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.

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

Answer 2

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.

Answer 3

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.