Hello, This is my first post in the forum. I just got a Seiki 55" 4k TV and I am trying to get my iMac to use it as a second display. I have the Accell Active mini-DP -> HDMI adapter and the computer recognizes the external display at the correct resolution. But the tv won't display anything. My iMac is a Late-2012 27" with all the max hardware config from apple. Any help?