My Galaxy S4 shows a black screen with clock. What is this? It looks like this:



I can't unlock or do anything with it. My Android version is 4.4.4 running CyanogenMod
This is the S-View cover mode. That's a cover with a piece of glass in it. Are you holding magnets by your phone? If there is no way to get out of it, you should restart your phone, or you can hold a magnet near your phone like the red dot: 



Hope my answer helps!