I solved the issue and this is how.
After lot of research and dozens of suggestions I decided to try something simple first.
My Samsung UE39F5500 was connected directly to the Internet, no cables apart from the power.
I opened the back of the TV and made sure everything was properly connected especially the highlighted part on the image. (shows how technical I am).
Thanks for your post re this dark band issue. You said "made sure everything was properly connected" but not that you found that a connection was lose or disconnected. Was there a lose connection? I had the same issue with my Samsung T27H390 It cleared it's self yesterday just by switching off and on again but today that didn't work. I read something about disconnecting hdmi cables and separate devices but the only connections mine has is LV power and terrestrial ariel so I pulled them out and plugged them back in and the dark band was gone. Hopefully this sorts the problem long term or at least doesn't have to be repeated too often.
any response to your post? I am having the same issue. It happened for the first time just a couple weeks ago and I had to do a manual software update but the same problem is back. dark screen on top of the picture, not software update available online.