1) First off, there's no iGPU in Ryzen CPU's. They will only be in the APU's when they come out, not CPU's. So there's no point in connecting to the motherboard to test video.
2) Has your MONITOR been tested with anything else?
- if not, attach it to another PC, or
- use a different monitor or HDTV with the PC
- use a VIDEO CABLE that has been tested elsewhere (i.e. HDMI cable from BluRay player)
3) Do you have a spare GRAPHICS CARD you can swap with the GTX1070 to test?
4) Confirm that the power cables go to the video card, and the motherboard for the CPU?
5) Double check the DDR4 sticks are fully seated as per the motheboard manual recommendation (for position of sticks).
6) Is the CPU fan spinning?