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    Third motherboard - PC still not working


    Hello, my problem began when I decided to build my first PC a little over a year ago (Dec. 2009):

    ASUS P7P55D EVO Motherboard
    Intel Core i5 750 CPU
    Nvidia GeForce GTX 275 Video card
    2 x 2GB Team Group Xtreem PC3-12800 DDR3 1600MHz 1.65v RAM
    1 TB Western Digital Caviar Black HD
    Cooler Master Silent Pro 1000w PSU
    Cooler Master HAF 922 Case

    1st Motherboard:

    The initial boot up was a success, and I proceeded to install Windows 7 64-bit and download all the updates, etc, without any problems. That same night I attempted to shut the PC off and turn it back on, however it failed to boot. Instead, the fans (including CPU fan) spun for a split second and then stopped, and that was as far as it got. I also noticed the CPU and RAM LED lights coming on during this brief time. The LED power light on the motherboard stayed illuminated as long as the PSU was turned on. If I turned the PSU or powerbar off and back on then I could press the power button and get the same brief fan spin up. I continued to try to power on my PC until eventually it actually booted up successfully a day or two later, without me modifying anything. However, after I left the PC unattended for a few hours I came back to see that it had shut itself off and it was back to doing the brief fan spin up when I tried to turn it on. I then tried deconstructing the PC one component at a time, and tried to power it up after each removal of a different component. It still exhibited the same brief fan spin up even when the mobo was out of the case with only the CPU and the PSU connected to it. I figured the problem had to be either the motherboard or PSU, so I tested the PSU with a multimeter and every voltage reading was correct. Therefore I decided it had to be the motherboard, and so I got a replacement.

    2nd Motherboard:

    The second motherboard seemed to work fine. This time my PC worked for about a year without any problems. About two months ago however, I came into my room to find that my PC had shut itself off and there was an electrical burning smell in my room. I found a charred spot on the mobo in the bottom left corner above the 1394a port. The computer was back to doing the same brief fan spin when I tried to turn it on. I RMA'd the mobo and got a third one.

    3rd Motherboard:

    Finally, I put my PC together with the third motherboard. It booted up just fine the time... Once again however, like my first mobo, the PC had shut itself off after being unattended for a couple hours. Now I am in the same situation with the fans spinning briefly whenever I try to turn it on.

    Conclusion:

    After three motherboards not working, I really have no idea what to do anymore. I'm starting to think that it may be something else that is the problem. Is it possible that the PSU could be the problem even though the mobo power LED comes on when I turn the PSU on, and that the multimeter shows correct voltages??

    Is it possible that it could be anything other then the PSU or mobo? I figured if it was the CPU, RAM or video card that was the problem that the PC would atleast partially boot up then make some beeping noises and the LED's would come on. But I could be wrong.

    Or there is the chance that I did actually get 3 faulty mobo's, if that's the case I guess I should think about buying a new model...

    I appreciate any advice, thank you.
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    What have you done to troubleshoot so far? I recommend piece-wise assembly--take your PC apart, and put it back together piece by piece. When the PC fails to boot, the last piece is usually the troublemaker.
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    Update


    Update: So far I have disassembled the PC 1 piece at a time and tried powering it on after each piece, but it never booted. After leaving the motherboard (with CPU still attached) out of the case for a day, I hooked it back up to just the PSU and tried powering it on. This time it worked. Then i shut it off, turned the PSU off and back on, then tried powering up the motherboard+CPU again and it failed.

    So basically whats happening is if I leave the PC turned off for a certain amount of time (about a day?), it will start up. But then it may either shut itself off after 2-3 hours or if i shut it off manually and then try to start it up again it will just do the brief fan spin up and not boot.
    This is exactly what my PC did with my 1st motherboard as well, but with my second one it worked for a year before it failed.

    I appreciate any advice, thank you.
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    Sounds very much like a PSU problem to me. A multimeter can tell you if a PSU is not working, but it can't tell you that it is working. Your multimeter places practically zero load on the PSU, the problem could very easily be something that only manifests itself under load.

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    When you are trying these things, is the motherboard in or out of the case? Shorts or loose wires can cause similar problems.
    Overall though I agree with E-Oreo, the PSU itself is definitely something to try swapping out.
    Last edited by karsh44; March 10th, 2011 at 06:14 PM.
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    Ya, the problem persists no matter whether its in or out of the case. I've also tried with and without the ram, videocard, cpu heatsink, harddrive, etc. Always the same thing, never starts unless I leave the power off for an extended period of time, then it starts up successfully once.

    I wish there was a surefire way for me to test my PSU, I guess I could just go buy a new one and if the same problem occurs I'll bring it back.
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    This definitely sounds like a PSU problem to me. More specifically, I wonder if a capacitor within the PSU itself isn't bad. This would explain the intermittent failure. I would replace the PSU and make sure you're using either a UPS or known good surge protector. You can get a UPS for fairly cheap (around 50-60 USD) and is well worth the investment in my opinion.
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    Alright thanks alot for the responses, I'll RMA my power supply and hopefully that'll fix the problem. I'm probably a pretty big idiot for not getting it replaced a year ago when this problem first started, before going through 3 motherboards. It's just I thought the PSU was working because of the multimeter test. Anyways once I get the new PSU I'll let you know how it works out.

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