Caran,I am puter illiterate like you. I tried googling black bar at top of screen,but it all depends on what computer system you have? Can't help sorry. Hope you get it sorted soon.
Hope you get your problem sorted out caran. When I had my screen problem, Hans Urbancka answered. Maybe he'll see your post later and pop in to help you
It's for the same reason you have a black bar, you have gone into 'private browsing' which doesn't store history or cookies so that no-one else using the computer can see where you've been. How you get out depends on what browser you're using and also if on a tablet etc.