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Troubleshooting a Computer that Turns ON, then Immediately Turns off


I press the button to turn the computer on, and the button lights up. Nothing appears on the screen and after about 2 seconds, the computer turns itself off.

I have pulled the power cord out and in, hoping that would fix it, but nothing happened.

Is there any way to turn the computer on?

There may be one or more of the following reasons, why your computer shuts down immediately after powering ON. You should go through each of the below troubleshooting steps to solve this problem.

1. Is this a newly built computer?

Did you recently build this computer? If yes, you should re-check your configuration. There may not be a problem with the hardware but something may not be properly configured, which is causing the computer to power off, after turning on.  Check your motherboard manual and see if the jumper settings, if any, are correct.

2. Has something inside the computer become loose?

Remove and re-insert all the cables, cards and RAM. A can also make the computer to power on and then immediately power off. This is a basic step in computer troubleshooting and more than 50 percent of the computer problems are due to or cards.

3. Do you hear a musical siren from the computer speaker?

If your computer gives a musical siren (a sound like dee-doo-dee-doo) for sometime, before finally powering off, it’s shutting down because of the overheat protection circuit. This may happen if there’s a loose or improperly connected heat-sink/fan, or if the fan becomes defective and stops. Check and make sure that the heat-sink is tightly fit to the processor (the CPU) and the fan connected and working at a good speed. Most motherboards have a CPU fan  speed monitor in the BIOS setup.

Here are some YouTube videos about properly installing a CPU, heatsink and fan:

Intel Cpu Install 

Installing a Processor and Heatsink

How to Build a Computer – 15 – Installing the CPU

How to Build a Computer – 16 – Installing CPU Fan

4. Is the 110/220v voltage selector switch at the back of the , set up correctly?

Most computer power supplies have a power selector switch at the back-side. The selected voltage is printed on the switch. Setting this switch to an incorrect voltage setting can damage the power supply and your computer. In most cases, your computer won’t turn on at all, if you set it wrongly, but it’s possible that the computer may turn on and immediately turn off.

The voltage that this switch should be set to depends on the country where you are. In some countries, it is 110v, in other countries, it is 220v. If you’re travelling to a foreign country with your computer, you should check this information before using the computer in that country, and then set the power supply switch accordingly, before you power up the computer.

If your power supply doesn’t have such a switch, it selects the voltage automatically and you shouldn’t worry about this. Click here to watch a video showing power supply removal. The voltage selector switch is clearly explained in this video.

5. Test the computer power supply.

A simple and easy way to test the power supply is to remove it from the computer and connect it to a working computer. Then, power it ON. If the computer boots up, the power supply is fine.

Another method to test the power supply uses a power supply tester.

You can get a cheap power supply tester for less than 8 USD. Click here for a list of power supply testers, which you can buy online.

If you don’t have access to another computer or can’t test the power supply in another computer for any reason, don’t want to spend on a power supply tester, here’s an easy way to test it yourself. But be careful, as shorting the wrong pins can have bad results. Also note that just the power supply fan spinning doesn’t always mean that the power supply is good, but if you can’t test it in other ways, this method can be useful.

On the ATX power connector, as shown below (a 20 or 24 pin connector, which connects to the motherboard), simply short pin no. 14 (in case of 20 pin connector) or pin no. 16  (in case of 24 pin connector), which is the green wire), to any of the (black) ground pins, which are 3,5,7,13,15,16,17.  These pin numbers are usually printed on the back of the ATX power connector, but even if they are not there, you can still recognize the green colored wire. There is only one green wire on the ATX power connector, so you can’t go wrong.

SNAP0104 SNAP0107 SNAP0108

Note: Shorting means connecting a piece of metal wire between two points.

For this, you may even use a U shaped, metal hair pin. Or use a paper clip straightened and made into a U shape, to short the two pins, as shown in the above images. After you short them with the paper clip or hair pin, turn on power to the power supply. The power supply fan at the back should start spinning. This tells us that the power supply is good.

Here’s a YouTube video about testing a computer power supply, using the above method.

If you tested the power supply as shown in the video above, and the power supply fan doesn’t spin at all, the power supply is dead or the fan is defective. It’s dangerous for non-technicians to try to replace the power supply fan, or repair the power supply, so just get a new power supply or use an old but good and working power supply.

6. Check and replace the power ON switch.

In rare cases, the power ON switch (on the front panel of the computer case), may be faulty.

You may test it with a multi-meter, which is set for the continuity test.  But an easier way to test the power ON switch is by plugging-in the reset switch’s connector in place of the power switch connector, on the motherboard. And then, power on the system.

If the computer powers ON with the reset switch, the power ON switch or the connecting wire is faulty. In any case, you can use the reset switch in place of the power ON switch, without physically replacing the switch. Just leave the power ON switch disconnected and use the reset switch on the front panel, to power ON the computer.

If you don’t like to replace the power ON switch with the reset switch, you can get a switch at electronic stores like RadioShack. A switch shown here may work for you, or you can search RadioShack for more such switches.

7. Does the computer power up with minimal parts?

Open up the computer and remove any add-on cards. Disconnect any drives including the hard drive and the CD/DVD drive. Also disconnect any external devices like printers, scanners or any USB devices.

The minimal parts needed to boot the system are – the motherboard with the processor, heatsink and fan, RAM, video card and the power supply. If the computer powers up in this way, then add the other parts, one at a time. Then, power up after adding each part. This way, you can easily identify the part or device that is causing the computer to shutdown. After identifying the problematic part, you can then test it in another computer, or replace it.

8. Does the motherboard power up on the bench?

Power off and unplug the computer’s power cord. Then, remove the motherboard out of the case, along with the RAM and the processor with its heatsink and fan. If there’s a separate video/graphics card, use that too. Also, remove the power supply and connect power to the motherboard. Don’t use any other card or device. Connect the output of the video card to the monitor and check whether this barebones system powers up on the bench. If it powers up this way, the problem is somewhere inside the case.

Here’s a set of images, showing the motherboard powered up on the bench:

Motherboard on bench (Image 1) Motherboard on bench (Image 2)

Here’s a set of videos, showing how to take a computer apart:

Part 1 Taking a Computer Apart

Part 2 Taking a Computer Apart

Part 3 Taking a Computer Apart

9. Is there an electrical short inside the computer case?

If the computer doesn’t power ON, even with minimal parts inside the case, power it off and unplug the computer from the mains. Then, closely inspect the computer case for any shorts. Usually, shorts are caused by screws that fall inside the case. These screws may come in contact between the motherboard and the case, and cause a short. The motherboard may also be touching the metal case at some place to cause a short. There could be other causes of a short and again, you should closely inspect the case.

Hold the computer case and gently shake it sideways. If there’s a struck screw, it may come loose by doing this. If you see a screw at a place where your hand can’t reach, use a pair of long nose pliers or tweezers to remove the screw.

If you tried to power up the motherboard on bench (see point no 8), and it powers up fine outside the case, an electrical short inside the case is most likely the cause of the computer not powering on. But at times, this may cause the computer to power on for a second and then power off immediately. If you’re unable to detect the reason of the short inside the case, you may want to take the help of a computer professional, or replace the computer case.

10. If you tried all the above steps and your computer still powers off, after turning on, you should take the help of a computer professional, or from a computer repair service. You can also take help from your computer manufacturer. Here’s a list of computer manufacturers and here’s a list of computer hardware device manufacturers.

  1. Geir
    April 5th, 2010 at 04:42 | #1

    Power supply is one of the major computer component taken for granted. I myself is guilty of this that consider it when its failing. :(
    Our computer is good as dead if power supply is not working… I saw a tech testing a power supply by shorting two pins on of the main power cables going to the mother board, its somewhere in the middle, just cannot remember the colors :)
    Thanks for the video again!

  2. Thomas
    April 7th, 2010 at 20:20 | #2

    Thanks for your video… this is very good way of presenting your ideas.

    Do you think Power supply may cause a video card’s capacitors to explode? Because I had two video card ended up with exloded capacitor on the same PC.


  3. May 14th, 2010 at 02:26 | #3

    It’s quite possible. Since the capacitors don’t have extra cooling fans, and can’t dissipate any extra heat if they get it somehow. I haven’t myself seen the capacitors on a video card explode, though I’ve seen many on motherboards bulge and some explode due to heat.

    Check if your computer lacks proper ventilation. You can also test your power supply, using a power supply tester. You can’t open the computer case, every once in a while to look for bulging capacitors! But they are the ones that may explode in the near future.

    Is your power supply regulated? Are you using a UPS or a power stabilizer of some sort? Is there something causing your video card to heat up? Is the video card’s fan working at a good speed?

    Is the card at such a place on the motherboard which gets high heat from other components? If yes, then you should try to change the card slot or add additional cooling methods to the card.

    Hope that helps.
    Support Tech

  4. Toby
    July 5th, 2011 at 23:29 | #4

    This is fantastic, my PC started doing the old “on for a second then off” routine last night and now I have some things to try when I get home tonight. There is still hope!

  5. August 20th, 2011 at 22:13 | #5

    Gee thanks for this wonderful post! You always give us great information. I personally find this interesting and really clears me off from my questions.

    I’m, beginning to know that I really learn lesser than I knew..


    thanks mate!

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