System is flashing White>Red>Green>Blue on boot.. CPU or Mobo? (more info inside)

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I've been working on computers for a very long time and am pretty knowledgeable, but this has me stumped and I can't properly debug the issue without spare hardware.

About 6 months ago, I built a new system with a Gigabyte Z170X Gaming 3 and a Skylake i7-6700k. Even on the very first day of my build, I had this intermittent issue where upon turning the system on, my screen would do nothing but slowly flash colors.. about 1 color per second, cycling through white>red>green>blue>black>white>red>green>blue>black>etc. No POST text, nothing.. just flashing colors.. so I can't get into the bios.

Normally, a few power cycles would get my video back. But over the weekend, my video card burned out.. and now when I try to hook the monitor up to the integrated graphics, I get this flashing issue every time I try to boot up. So I have a hunch that the problem is directly related to integrated graphics.. and when the issue was happening in the past, it's because the bios was choosing the wrong GPU and rebooting would get it to correctly choose my dedicated graphics.

My OS boots up in the background, I can see on the HDD indicator LED.. but the screen just perpetually flashes colors.

I don't have a spare 1151 CPU laying around, so I can't test that to rule out the issue. What does this seem would be the most likely cause? I'm leaning towards the motherboard.. but at this point it's a wild guess. I've cleared the CMOS and no luck.

Stupid Gigabyte support is only open M-F 8-5... when I'm at work.. so I can't do much on the phone with them.

Here is a crappy video of the issue, pardon my sniffling: https://www.dropbox.com/s/0dq2rqrhh2dt4g1/VID_20160424_122116.mp4?dl=0

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That is what your monitor does when it does not get a signal. I assume, that when you turn it on and unplug the signal cable it will do the same.

-> I think your GPU isn't working properly;

There we go, sorry to hear that.

Does your mainboard have the GPU unboard, becaus the i7 - 6700K does not; I assume the moherboard does neither; the graphics ports are there for Intel CPUs with GPU integrated; but yours does not have that, so there wont be any signal from the VGA, DVI-D, HDMI or DP outlets on the mainboard;

I would say, that your graphics card had some problem right from the beginning (not starting correctly)

Get a replacement GPU (lend one? buy one) than you should get video again.

[EDIT] the Gigabyte Z170X Gaming 3 has no GPU on the mainboard; so there is simply no graphics adapter in your system now.

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Well I just figured it out shortly after posting. I tested a spare 1080p monitor and it worked. So I was thinking maybe it was an issue with my main monitor being 2560x1440.. Checked the mobo manual and sure enough the board only supports up to 1920x1200 over Dvi-d with Intel graphics, 4k over hdmi. That was my issue. My main monitor unfortunately doesn't have hdmi.. So I'll have to use my spare 1080p while I wait for my video card RMA to go through

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Ohh I am sorry, I was not aware that the i7 actually has the Intel® HD Graphics 530 built in. I was pretty confident that the K skew did not have.