Z170X-Gaming 7 won't boot with two monitors connected

This machine is one I built recently.  I want to use the two video ports to run two monitors.  The problem it is having is when both the DP port and the HDMI port are connected to monitors, it hangs at the initial boot screen, the one that comes up like 2 seconds after I press the boot button and has all the F key descriptions at the bottom of the screen.  If I unplug the HDMI cable and press the boot button, boots fine.  If I reconnect the HDMI cable and "Restart:", it boots fine and runs both monitors fine.  It is only when booting from a shut down with both the DP port and HDMI port connected to monitors that it hangs at the F key screen.

I have been using a HDMI to DVI adapter to DVI cable to run the 2nd monitor.  It is this cable that when I unplug it, the machine boots fine.

Alternatively, when I unplug the DP port cable and leave the HDMI to DVI connected, it will boot fine.

And another alternative, when I boot it with one cable plugged in and then wait until it gets past the F key screen, the plug in the 2nd cable, it boots fine and both monitors display.

What can I look at to resolve this issue?

Mobo is Z170X-Gaming 7
Bois Version F6
Bios date 12/16/2015
Bios ID 8A09AG0A

One more thing I tried and this may be a whole other issue, I bought a HDMI to DP cable and tried running from the HDMI port on mobo to the DP port on the monitor, but get no signal.  Wonder if that is just a function of the HDMI cable from mobo port won't run the DP port on the monitor?