Computer ran, installed windows, turned off, won't turn back on. HELP

Elvirth

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Sep 26, 2011
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Ok, so....

Helped my friend build a PC tonight. We attempted to build it a couple weeks ago, but his mobo was DOA so we ordered a new one. Asus z170 Pro Gaming/Aura. I post tested everything before assembly, all components worked fine. We finished the build, then shut it off after installing a bunch of things so I could unplug an optical drive used for installing the OS. After that, the PC would apparently boot, but there was no display. No error lights. The board does not have a post code display or speaker, so I pulled the speaker out of my rig to help diagnose what was wrong. Upon plugging the speaker in, pressing the power button did NOT cause the computer to boot. All that happens is an audible pop in a pair of headphones plugged into the rear audio jacks. This build has been bugging us for two weeks now, I refuse to believe we got two lemon mobos in a row but that might be the case. Please advise.
 

Elvirth

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Sep 26, 2011
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Ok.... update. Unplugging the PSU entirely revealed that somehow, power was being fed to the motherboard through the displayport connection from the monitor, through the graphics card. Unplugging the graphics card and running the displayport cable to the onboard port caused the system to actually start up, and give a post beep (I reconnected the post speaker), but still no display. Really not sure what to think at this point.

UPDATE 2: Swapping the displayport cable for an HDMI cable resulted in perfect boot, with or without GPU. Still not sure what the hell is going on. I've never seen a monitor feed power into a computer via DP.
 

Elvirth

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Sep 26, 2011
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Ok... THIRD update. After swapping out for an HDMI cable and getting a perfectly ok boot, we recreated the original conditions of the build, including a different DisplayPort cable (which was not helping before), and NOW EVERYTHING WORKS FINE. I legit do NOT understand what the hell is going on here.
 

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