Troubleshooting my first startup with my custom built computer.

Hey all - sorry if this is in the wrong forum, so please feel free to move it, but I need help starting up my PC.

First go around:
I places all of the components and made all of the connections, and went to turn the PC on. The fans were working, the green mobo light was on and it seemed like I was smooth sailing. The problem was, there was no display. I tried it with another video card, different RAM, etc.. no luck.

Then I released I had idiotically overlooked placing the ATX 12v power supply into my mobo (the power supply is 6 pin, but the input for the CPU power is 4 pin). Now, I try to turn it on and it turns on for a split second then quickly powers off. I tried reversing the connectors for the power supply and the reset switch on the LEF board but no luck. Any ideas what could be causing this?


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  1. The 6 pin connector methinks is a PCI-E connector, you want the 4 pin or 8 pin EPS connector. Are the cables not labeled on your PSU ? Read your PSU and MoBo manuals thoroughly for a description of all the connectors.
  2. Well, there is a 4 pin connector, but that is augmented to the 20 pin connector that goes into the main 24 PIN mobo supply. So all I have left are 2 6 pin connectors (one that goes into my video card) and the other I used to go into CPU power.

    There is no 4 or 8 pin connector provided with the power supply.

    It is odd that it will boot up when the power supply isn't in the CPU slot, but will shut off immediately if it is.

    Any idea why the power supply wouldn't come with a 4 or an 8 pin connection?
  3. You're looking for the square 4-pin connector. Any out of the psu will do.
  4. The 6 pin can fry the mother board if plugged in the 8pin holes. every PSU has 12v ATX 4 or 8 pin unless its hella old.
  5. What PSU do you have?
  6. daship said:
    The 6 pin can fry the mother board if plugged in the 8pin holes. every PSU has 12v ATX 4 or 8 pin unless its hella old.

    And if it is that old, it won't have the six pin PCIe power connectors. The PCIe connectors are wired differently from the CPU connectors. Interchanging either will result in a 12 volt short straight to ground. If you have a good PSU, the Overload Current Protection (OCP) circuits will nondestructively shut the PSU down.

    Like clarkjd asked, "What PSU do you have?"

    Time to start troubleshooting. First look at this to see what mistakes you made:
    Build it yourself:

    Then :
    Work systematically through our standard checklist and troubleshooting thread:
    I mean work through, not just read over it. We spent a lot of time on this. It should find most of the problems.

    If not, continue.

    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: 5 volts always on. Tolerances are +/- 5% except for the -12 volts which is +/- 10%.

    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.

    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.

    If this seems too complicated, I'd suggest finding a more experienced friend to help.
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