I know there's some threads about this already, but have not found a solution to the problem. I bought a monoprice mini display port to mini display port cable to try to connect my SP3 to my 2009 iMac 27inch so I can do some photo editing but when I plug the cable in it the iMac just shows a black screen. After several seconds it reverts back to it's default OSX desktop. Is there something I have to enable to get the screen to mirror over or extend over? Or is it something I have to enable on my iMac? I thought it was plug and play.