I have been retrogaming with Octapolis on an emulated Commodore 64. Starting up the game presents a menu offering a choice between one or two players, and between music and sound effects. But I don't know how to use the menu. It does not respond to anything other than the fire button, which starts the game with one player and sound effects. Moving the joystick, pressing the cursor keys, or pressing space doesn't do anything. How is this supposed to work?