Black square on screen

I have a Panasonic F87. During the previews on a DVD the picture is fine. However, when the menu screen comes up a black square appears in front of the picture. You can see a small portion of the movie behind it. But the features are not accessible, such as adding captions. Sometimes, after you push the play button, you can see the movie, but most times you cannot. Sometimes you can advance the movie and the box disappears, but often it does not. Sometimes in the black box, characters such as @@@@@@@@ will appear. What can I do to get rid of the square so we can watch movies? Appreciate any help you can give.