Newly Built PC turns on without CPU cable, doesn't turn on with CPU cable plugged in

IMightBeABagel

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Aug 9, 2015
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I am building a PC for my friend and by doing some tests I found out that the PSU and the motherboard are not dead. I am able to get the PC started but only if the 4+4 pin CPU cable is not plugged in. The PC beeps, and the CPU fan, GPU fan, and system fan all start as well as the HDD and ODD. Only the front panel LED lights up/does anything while the 4+4 pin is connected.
So I've determined that the CPU does not need this connector, though that does strike me as weird. Here are the specs:

http://pcpartpicker.com/list/TDC8M8

However, when I turn on the PC (brand new, doesn't even have Windows installed) there is no display on the monitor. The LED goes to orange (signaling that there is no display) despite the DVI-D port being plugged in from the monitor to the 750ti and power being delivered to it from the wall. Could the monitor be dead? If so, how can I find out?

TL;DR: New PC won't turn on without the 4+4 pin connector not installed, and when I do that there is no display on the monitor.

Any responses are appreciated. Thanks!
 
The motherboard 4/8 pin cpu lead is often not needed at all.
It is there to handle the added power that might be required with fully populated expansion slots or a higher wattage cpu or overclocking.
Your motherboard manual should say something about that.

The fact that you seem to progress further with it disconnected suggests to me that either there is a problem with the psu 4/8 pin lead or the motherboard has a problem with the 4/8 pin socket.

I suggest you remove the motherboard from the case and test with minimal components.
That eliminates any issues from possible case shorts.
Attach the monitor to your motherboard integrated outputs.

You can start the motherboard by momentarily touching the two PWR pins of the front panel header with a screwdriver.
 


What is a case short? And also, are the PWR pins we're talking about the PWR LED + and - ones?
 
Sometimes you can get a short where the motherboard touches something in the case and causes a short.
It might be a mounting hole with solder nearby or such.
Just put the motherboard on a table and attach all the parts.

Do not use the graphics card in case that is part of the problem.
This is called "breadboarding" I do this first to test the parts on every new build.

Your front panel pins will have two that are called just PWR that are used to start the pc. They are not polarity sensitive.
The PWR-LED pair have a + and a - If you connect them reversed, no problem, but the led will not operate.

Do not connect any front panel pins for testing purposes.
Your motherboard manual will identify the PWR start pins. Look carefully to orient the image; they can be confusing.
You will get strange results if the led pins get wrongly connected to the reset pins.
 


The front pane header will have several pairs of pins.
PWR
Reset
PWR-LED
HDD activity.
Only the les pins are polarity sensitive. You need to get the + and = connected properly or the led will not light.
 


Okay, I have done what it said. No front panel connectors attached (including HD Audio and the USB 2.0 header) When I plugged in the PSU to the wall and an HDMI cable from the motherboard to the monitor and flipped the PSU switch on, the PC did start. The fans started, the CPU fan began to whir, stuff that would indicate that it did indeed boot up. But there is still no display. I'm ready to return everything and give the guy his money back. I've never encountered anything like this before.