Open the music box. How you open it depends on the type of music box you have. Either open the glass lid, unscrew the fixed glass lid or slide the wood panels. Do not apply too much pressure to the panel as you open it, as this can break the music box.
Move the external start button to the left. Loosen the nut on the inside of the music box and adjust the metal panel. There should be a small space between the starter button and the large metal piece near the teeth of the music box.
If the music box will not stop playing, press the inside metal latch downward. Move it away from the springs inside the music box. Gently press the latch down, or bend it down with a plier.
Perform these steps regularly to ensure that your music box is well maintained. Once your music box malfunctions, it is likely to happen again.