XB270HU no signal after BIOS POST

Hello, just got my new XB270HU and there's no signal after the BIOS POST messages have been displayed. The BIOS messages are all displayed correctly but then just at the point where you would see the "Starting Windows" graphic it goes black.

My GPUs are dual GTX970 in SLI.

I've tried a different monitor (an HP) using the same DisplayPort cable and it works fine.

What's odd is that if I boot up the computer using the HP monitor and then swap over to the XB270HU once Windows has started it works perfectly.... Also, if I do a dual monitor setup, with HP running on HDMI and the XB270HU on DisplayPort it works as well. But what's weird here is the BIOS messages appear on the HP along with "Starting Windows" but then the Acer becomes the primary as soon as Windows has started.