Which part is the broken one?

Hi, I've got a problem which really got me annoyed and confused. I've been putting the parts together for my own computers quite a lot of times, and I know how to read instructions so that's not where the problem lies.

I just bought the parts for an intel i5 computer, with the i5 760, a 700W OCZ modstream psu, the P7P55D LE motherboard and an ASUS Geforce GTX 470 with the requirement of a 550W psu. After I put all of this together, I plugged it in and tried starting it up. That didn't work for some reason. After removing all my harddrives, rechecking the pins to the power-button (yes, the green power indicator light was shining in all its glory), I tried removing the RAM, the graphic card, and finally I tried when disconnecting the 8-pin cpu power cord. It was when I did this, that the computer powered up finally. I've been troubleshooting a bit on my own and with everything plugged in but this cord, everything powers up.

My question is, how do I figure out if it's the motherboard, the PSU or the i5 CPU that's toast?
Would it not power up if it was the cpu that was broken? Or do I need a more powerful PSU? Can the motherboard have a cpu-thingy short circuit?

I appreciate all advice and help.
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  1. Never mind, tried the troubleshooting guide, and using deduction I figured out the cpu is most likely fried, since I put everything on a bit of cardboard and it powered up, but I got a black display. Tried one RAM-stick, and three different graphic cards.. Bloody faulty cpu.. fml
  2. ^ You sure the CPU is faulty ? That is pretty rare IMO...
  3. Like gkay said, it happens but it is very rare.

    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 beep 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:

    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.

    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.

    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.
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