3rd Screen Won't Go Away

I've been having issues in my dual screen setup when trying to edit in Davinci Resolve.

Basically, the video doesn't show up in Resolve.

I've posted in the Black Magic Design forum AND at MacRumors forum but haven't figure it out.

Any idea what to do here? I think the problem lies in the MacBook pro's screen not shutting down when I do the 2 monitor hookup.

Sabrent Displaylink dock where the 2 monitors are connected.