Computer restarting over and over

Hi all!

So my friend told me that his computer wasn't working anymore. He said that it is restarting over and over.

So he gave me his computer and now, I can't even go in the BIOS. I press the button to start it and the fans start and restart and restart.... over and over. I tried with a different HDD, ram and GPU and it still don't work.

So what you guys think is the problem? The mobo? Processor? He told me that the tech tried with a different PSU and it has the same problem.
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  1. Best answer
    When you are asking for help, always start off with the system specifications.

    It sounds like you have either a bad power supply or a shorted component.

    It sounds like the system is trying to power up, then the PSU detects a short and electronically shuts itself down. When that happens, the PSU load drops, and the cycle repeats.

    The following is an expansion of my troubleshooting tips in the breadboarding link in the "Cannot boot" thread.

    I have tested the following beep patterns on Gigabyte, eVGA, and ECS motherboards. Other BIOS' may be different, but they all use a single short beep for a successful POST.

    Breadboard - that will help isolate any kind of case problem you might have.

    Breadboard with just motherboard, CPU & HSF, case speaker, and PSU.

    Make sure you plug the CPU power cable in. The system will not boot without it.

    I always breadboard a new build. It takes only a few minutes, and you know you are putting good parts in the case once you are finished.

    You can turn on the PC by momentarily shorting the two pins that the case power switch goes to. You should hear a series of long, single beeps indicating memory problems. Silence indicates a problem with (in most likely order) the PSU, motherboard, or CPU. Remember, at this time, you do not have a graphics card installed so the load on your PSU will be reduced.

    If no beeps:
    Running fans and drives and motherboard LED's do not necessarily indicate a good PSU. In the absence of a single short beep, they also do not indicate that the system is booting.

    At this point, you can sort of check the PSU. Try to borrow a known good PSU of around 550 - 600 watts. That will power just about any system with a single GPU. If you cannot do that, use a DMM to measure the voltages. Measure between the colored wires and either chassis ground or the black wires. Yellow wires should be 12 volts. Red wires: +5 volts, orange wires: +3.3 volts, blue wire : -12 volts, violet wire (standby power supply): 5 volts always on. The green wire should also have 5 volts on it. It should go to 0 volts when you press the case power button (this is also a good way to test the power switch and the associated wiring), then back to 5 volts when you release the case power switch. Tolerances are +/- 5% except for the -12 volts which is +/- 10%.

    The green wire should be 5 volts whenever the PSU is plugged in and the PSU switch is on. It will drop to about 0 volts when the case switch is pressed and go back to 5 volts after it is released.

    The gray wire is really important. It should go from 0 to +5 volts when you turn the PSU on with the case switch. CPU needs this signal to boot.

    You can turn on the PSU by completely disconnecting the PSU and using a paperclip or jumper wire to short the green wire to one of the neighboring black wires.

    A way that might be easier is to use the main power plug. Working from the back of the plug where the wires come out, use a bare paperclip to short between the green wire and one of the neighboring black wires. That will do the same thing with an installed PSU. It is also an easy way to bypass a questionable case power switch.

    This checks the PSU under no load conditions, so it is not completely reliable. But if it can not pass this, it is dead. Then repeat the checks with the PSU plugged into the computer to put a load on the PSU.

    If the system beeps:
    If it looks like the PSU is good, install a memory stick. Boot. Beep pattern should change to one long and several short beeps indicating a missing graphics card (unless you have on board graphics available). In that case, remove any card and connect the monitor cable to the motherboard connector.
    Silence, long single beeps, or series of short beeps indicate a problem with the memory. If you get short beeps verify that the memory is in the appropriate motherboard slots.

    Insert the video card and connect any necessary PCIe power connectors. Boot. At this point, the system should POST successfully (a single short beep). Notice that you do not need keyboard, mouse, monitor, or drives to successfully POST.
    At this point, if the system doesn't work, it's either the video card or an inadequate PSU. Or rarely - the motherboard's PCIe interface.

    Now start connecting the rest of the devices starting with the monitor, then keyboard and mouse, then the rest of the devices, testing after each step. It's possible that you can pass the POST with a defective video card. The POST routines can only check the video interface. It cannot check the internal parts of the video card.
  2. need your specs please
  3. There is a short

    Probably in the psu , or more likely the on button on the case

    remove the connector to the power switch and use the tip of a screwdriver to momentarily connect the two power pins .

    if it boots its the switch if it behaves the same its the power supply
  4. Oh yes I forgot the specs. I can't tell more for the moment because I don't have the specs from my friend.

    Mobo: Asus P5B
    Ram: 2x OCZ PC2 6400 1GB DDR2
    Video: Asus, ???
    Proc: Intel Core 2 Quad ???
    PSU: Antec 650 watt
    HDD: 320GB western digital

    There is a short

    Probably in the psu , or more likely the on button on the case

    remove the connector to the power switch and use the tip of a screwdriver to momentarily connect the two power pins .

    if it boots its the switch if it behaves the same its the power supply

    Just to be sure, do I remove the connector on the MOBO or the one on the power button? Sorry this is maybe a newbie question, but I don't want to do a bad move :P
  5. from the mb end

    just a touch both mb pins at the same time with the tip of a screwdriver to start
  6. I would also check the motherboard for any bulging or leaking capacitors. this is often how a system with bad caps will behave and I've found s few instances.of it happening with that board
  7. So the problem isn't the power button. I'm gonna try a fully functionnal PSU tonight.
  8. So I tried with a fully working PSU and nothing to do. The computer still have a short. I tried to put the PSU, GPU and ram on another computer and it works great. So it's either the Proc or the Mobo. Is there anything to do with that? or the only solution is to buy a new Mobo?
  9. Have you checked your mobo for bad capacitors yet? unksol brought up a good point earlier about how a bad mobo can behave this way. I had an old Dell laptop that did the same thing when its mobo died, which means you might need to buy a new one.
  10. Best answer selected by joce21.
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