The black square / box is associated with the text function on the TV even although the TV might not be receiving it, and this is a procedure that gets over the problem on "some" chassis. If you have a "closed caption" button on your TV's remote control press it until the black square disappears. (This sometimes marked "CC" on remote) However if you don't have that button on your remote control try this / Bring up the menu and highlight "closed caption", to access this menu press the "volume +" button. When you enter this menu it will say "mode text" Press the "volume +" button until it says "mode off", then press the "channel -" (minus) button and highlight "finish".