Using Biostar Racing Z270 GT6:  set maxTOLUD, did not set security settings (no option in Z270).

A few questions and problems::

1) Plugging in a second GPU (via risers, 1st GPU also via risers) causes the motherboard to black screen on boot.  Here's a teamviewer screenshot of how it looks like (display stopped working when a 2nd GPU came in, had to remote in with teamviewer).   http://imgur.com/a/H5flW

2) The closest PCIE to the CPU is a 1x, then a 16x.  Which slot is considered my "primary GPU"?  Is it the 16x?