Check where you have the cable plugged in again vs the port you have selected for the input in the menu.
The late model Samsung's I have seen do not have a port labled HDMI/DVI 2 on the rear of the set.
They do have HDMI/DVI 1, HDMI 2, HDMI 3...
Even if you're sure you have it on the correct input, change it to each of the HDMI in turn leaving it on each one for 15 seconds or so.
The next step is to unplug everything and replug it all back in making sure the connections are tight - even though they look and feel good currently.
Have you tried moving your mouse off the screen of the Mac in all directions and onto the screen of the TV?
edit to add:
"after" the above, then try a different HDMI port on the TV. Preferably one you are already using with another device, so that you know it works.
Next step is to try a different adapter/cable and TV.
In this situation, where the Mac is recognizing a screen is attached and providing you with a window for adjusting the resolution of the 2nd screen but still no picture, my inclination would be faulty adapter/cable.