I've got a late 2013 iMac running OS X El Capitan and am trying to get a second screen for work. Its a Samsung LED Syncmaster SA350 Series (Plug & Play). When I plug it in, nothing but a black screen displays, even though its on and my Mac detects it (I can even drag windows over there etc). I'm connecting DVI-->HDMI.
Most of the answers I've found on this say to update the firmware, but It doesn't look like I can do that on my Mac. Is there any way to get this screen to start displaying other than through a firmware update?