Before a sound/music can be played, you have to first ensure that the player interacted with your game (a simple click/touch on the screen is ok to unlock audio). This is a limitation of browsers and cannot be worked around. In your final game, it’s recommended to have on your first scene a “Press any key or touch the screen to continue” message.
Is this in the browser or with preview on your PC? If the browser, then what @yorik wrote applies. If it’s in preview, then maybe setting the initial volume to 1 may resolve it.
Otherwise, try using play sound instead of play music.