New motherboard - computer wont power up...

Received my RMA replacement for my previous defective motherboard (memory slots didn't work right, CPU socket was fine), which at least ran, and now in this build, the motherboard wont boot.

The first time I push the power button (after turning the PSU on), the lights flash for a half second and the fans barely start to spin, but then it goes dead. Subsequent presses of the power button do nothing.

I know it is not the power supply since it worked with my previous motherboard just fine, and also worked with the paper clip test (paper clip to green and black wire powers up the PSU fan). Removing the ATX 2x4 connector cause the motherboard to power on for a half second and then turn off repeatedly until I turned the PSU off. I also tried to reconnect the ATX plugs multiple times to no avail.

Also, have tried reseating the CPU, and have replaced the CMOS battery and cleared the CMOS.

I am running the computer outside the case, with the bare minimum set up needed to boot, so there is no possibility of a short.

Any ideas on why I can't power up? Would hate to have to RMA this board again and wait again!

GIGABYTE GA-P55A-UD3 (Rev 2.0)

OCZ ModXStream Pro OCZ700MXSP 700W

Thanks for the help!
9 answers Last reply
More about motherboard computer wont power
  1. Do you smell anything that might have burnt out?
  2. Quote:
    Memory slots didn't work right?

    My only suggestion to you is to take it to a professional and have them put it together for you.

    Ha, I have been building computers for 15 years. Its not a lack of experience.

    It was the 4GB only 2GB usable issue, but there were no pins bent or misaligned.

    There is nothing burnt.
  3. Thinking of the "possibilities" - your PSU is multi-railed and seems to lack Japanese capacitors, so I'd either try another PSU or use a voltage meter to double-check. Next, what is the part number of your RAM?
  4. It's a possibility that you got another bad mobo.
  5. Whatever happens after you pull the CPU power plug is meaningless. System will not try to POST without a CPU.

    The paperclip trick with PSU can tell you if the PSU is bad, but it cannot tell you for certain if it is good.

    Work through our standard checklist and troubleshooting thread:
    I mean work through, not just read over it.

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

    Breadboard with just motherboard, CPU & HSF, case speaker, and PSU. You do have a case speaker installed, right? If not, you really, really need one. If your case or motherboard didn't come with a system speaker, you can buy one here:

    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:
    At this point, you can sort of check the PSU. Try to borrow a known good PSU. 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.

    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. Assuming compatible memory, the beep pattern should change to one long and several short beeps indicating a missing graphics card. Silence or long single beeps indicate a problem with the memory.

    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.

    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.
  6. "Personally" the paper-clip test if done wrong can destroy your PSU. Do it to yours at your own risk. Get a Digital Multimeter at Radio Shack for $20-$30; Model: 22-182 or 22-813.

    A bad PSU can damage or destroy anything its connected to: MOBO, GPU...
  7. I agree take it to a pro. Just because you built a Pc 15 years ago don't make you an expert.
  8. Thank you PSC for the very helpful post.

    PSU is fine, worked without issue with my previous motherboard. Dont think its possible to go bad sitting idle and not plugged in for two weeks.

    I am breadboarding. I am using a speaker, but there is no sound. I dont think the motherboard is powered on for long enough for it.

    Pretty sure its just a bad motherboard. I got a new one today and am going to try tonight.
  9. New mobo works, definitely the motherboard...
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