M4A785-M Bundle, Turns on for a few seconds, shuts off.

This is a first from scratch build for me, but i DO know what i'm doing, i'm not completely clueless. It was a barebones kit from CompUSA, so all parts are compatible. The cpu is an AMD Phenom x4, the mobo is an Asus M4A785-M, the HDD is a 1.5tb Seagate Barracuda, the dvd-rw is LG, the cpu fan is a HUGE coolermaster hyper n520, the RAM is 2x 2048 ddr2, and the psu is a 450w that came with the case. i have everything connected, properly (as best to my knowledge) and i attempt to turn on the computer with the front power switch and nothing happens. the only time anything happens is if i turn on the switch on the back of the psu, and it turns on for a few seconds, and then it shuts off. all parts are fresh out of the packaging, so i don't know what it could be, besides if one part is defective. If that's it, then i don't even know where to start to narrow down to what part. Any help is GREATLY appreciated!!!
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  1. When you are asking for help, always start off with the system specifications. Then, is it a new build that has never worked or is a previously working computer that now doesn't. Is it an upgrade that you are having problems with?

    The Great Carnack is dead. We need you to tell us these things. Each of the three problems about require somewhat different troubleshooting techniques.

    However, onward to some systematic troubleshooting techniques.

    Work 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 beeps patterns on Gigabyte, eVGA, and ECS motherboards. Other BIOS' may be different.

    Breadboard - that will help isolate 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.

    Motherboard LED's mean very little. When on, all they are telling you is that the computer os plugged into a live power socket and the PSU is switched.

    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 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.

    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 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.
  2. Do you have the 4 pin CPU power connector connected?

    Sounds like you have a short. Extra standoff or wrong wire connected.

    Could be a dead PSU also. You can test that with a $10.00 PSU tester or the above paper clip method.
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