display

Hi there,

Im trying to hook up an external monitor (HP) via thunderbolt to DVI. When I connect it, I get the opening screen in all its glory, looks pretty sharp as well I might add. But...no other functionality other then the wallpaper. th iMac pro laptop screen functions as normal , but the external seems to be locked to the wall paper.

I am obviously missing a step...who can help direct me?

Colin