How to tell if bad CPU or Mobo on new build.

So I'm working on a new build for a friend and I ran into a bit of a snag. This isn't my first build and I've double checked and triple checked the power connectors to the Mobo but I can't seem to get it to post or even react at all. I have the cpu power connector and the mobo power connected and I've set up only one stick of ram and added the CPU and cooler and plugged in the CPU fan.

However, whenever I short the connector to boot, nothing happens. No beeps, no cpu fan, not screen prompt. So at first, I pulled the video card off the board to see if it was a lose connection and shorted it again. Again, no beep or reaction. So then I thought maybe it was a faulty PSU even though the short was sparking. So I plugged the mobo into my computers PSU. Once again, no post.

So I ruled out the PSU. However, I can't find any reference to help me decide what the problem could be. Will the CPU fan still function even if the CPU is faulty or will it not react like in this situation or is this a sign of a bad mobo? I've checked the CPU for bent pins and found no problem, it slid right in perfectly. I just can't figure out a way to rule out either the CPU or the Mobo independently without some way to distinguish the failure. I would remove the CPU from my computer and put it on the board but I don't have another CPU that matches the socket type.

I will also add that I was having some difficulty seating the 24-pin power connector into the Motherboard. It would fit but trying to get the connector completely down was a hassle and getting it out was a hassle with both PSUs. I thought maybe it was just a shallow connector at first but without seating it all the way down, it wouldn't even short (not really a surprise).
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  1. Best answer
    Unplug the 4 or 8 pin from the board, see if that powers on.
  2. Nope, still doesn't power on. Actually, it didn't short either. So it's safe to bet the 24 pin is faulty. Thanks. Such a simple solution and yet it's diagnostic value is so high. Now I feel bad I didn't think of it first :p
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