When I build a system, I assemble the CPU, RAM, & PSU. Then I use the integrated graphics and the video output on the motherboard to see if it boots up. Then I assemble the rest of the system. Then load the operating system. And lastly I install the graphics card after verifying that everything else works.
So, not being able to use the integrated graphics throws a wrench in the way I normally build a PC.
Without any motherboard diagnostics or monitor, it is going to be difficult to narrow it down. From my understanding, the only new parts are the motherboard and processor.
Can you install the old processor in the new motherboard? If it works with the old processor, then you can return the 2700X.
Alternately you can install the the old processor in the old motherboard (assuming it works) then load the latest BIOS. And then install the 2700X in the old motherboard. That will test all of the parts together other than the new motherboard. And you said that the graphics card worked with the old motherboard.
That would isolate the problem to the new motherboard, and get your PC running in the mean time.