I had same problems, as well as sound going off while watching certain Netflix shows. First: sound issues. I found that when watching certain shows, I could watch a few minutes, then sound would go off. To resolve this, while playing the show, I hit the DOWN arrow so that it highlights the AUDIO AND SUBTITLES button..., then I see that ENGLISH (5.1) is selected, and then I select the one above it that just says ENGLISH, that episode will start again and the sound should work FINE!
OK, black screen. After 3 hours of trying to get netflix to resolve it, factory resetting, doing all sorts of things etc., I called Samsung - was on hold for 40 minutes after someone told me to wait a minute while she found someone - then I was disconnected. I called back, pretty frustrated - vented on the poor guy who then answered, and he remotely dialled in to my tv and fixed it within a minute. This is what he did.
1. Hit the smart hub button, so that all the apps pop on the screen (there are different ways of doing it - choose the way you normally do it, and make sure all the apps are on the screen)
2. move the cursor up so that you are highlighting the netflix app. DO NOT PRESS ENTER. JUST MAKE SURE NETFLIX IS HIGHLIGHTED. REPEAT. DO NOT TRY TO OPEN NETFLIX. JUST MAKE SURE THAT NETFLIX IS HIGHLIGHTED. THAT IS CRUCIAL.
3. hit TOOLS
4. scroll down to reinstall and select reinstall. it will say "installing" on top right hand side
once done, NETFLIX SHOULD WORK!!!!
If not, DO try calling Samsung and ask for someone who can remotely go into your TV - they WANT it to work for you and will talk you through how to do it.