Hello everyone.
I hope this is the right place to consult about this issue I'm having.

my spec is (at least the parts which I think relevant to this case):

CPU: Intel Core i7 4790K 4.0Ghz 8MB L3 Cache s1150
Motherboard: Asus Maximus VII Ranger
Memory: G.Skill Ripjaws-X 4x8GB DDR3 1600Mhz PC3-12800 Kit CL9-9-9
Graphic Card: Asus GTX970 STRIX OC DirectCU II 4GB
PSU: Corsair TX 750W PSU
Monitor (Display Port): Dell U2414H
Monitor (HDMI): Samsung B2330HD

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About a week ago I've added the Samsung monitor which is used also as TV on my desk (lack of real estate to place monitors), the Samsung is connected via HDMI to the PC and to the Cable box.

The Dell monitor which I'm using as main display for my PC is connected via DisplayPort cable.

Before I've created this setup I had another non-TV dell monitor which was connected with DVI cable and my current main Dell display was connected via HDMI cable.

Since I've connected the new DisplayPort cable I can't boot either from sleep\hibernation or fresh boot from off state while the DisplayPort cable is connected. I can boot with the HDMI monitor connected alone and then connect the DisplayPort while I'm logged in into Windows and while not going into sleep or shutting down everything works well - I can actually reboot the pc and it will work.

Further investigation shows that when I try to boot with the DP cable and HDMI connected I get blank screen (both monitors) and no audio\beeps from the bios post process. Then I shut down the PC using the power button and boot again with only the HDMI cable connected to the monitor then I get a BIOS error screen notifying me that the OC has failed and I need to hit F1 to set my bios settings. (Note: I only use XMP for the RAM).
If I just hit F1 and close the BIOS without changing anything the PC will boot normally and I can even connect the DP cable and the monitor will work.

This phenomena was weird at first, and I've tried to replace the DisplayPort cable, boot only with the DP cable connected and even tried to reset my Bios settings (I got latest UEFI version installed). Nothing seems to work.

Using my Googl-Fu skills I noticed a thread, where people said it might be due to the fact the DP is "new" and transferring power as well as audio\video input which cause on some motherboards malfunction during boot because of some PCI-E power configuration issue.

I could really use your input on the matter and thanks in advance for your help!

EDIT:

Further testing,
on my Dell display management OSD I enabled DisplayPort 1.2 > didn't help.

forgot about checking out my motherboard OSD display for POST code, seems the PC while the DisplayPort is connected during boot freeze with code of 77.