Welcome to the forum. There could be a zillion things, so we really need a bit more info. What have you tried so far? Have you confirmed your headphones and/or headphone adaptor (if you use one) are ok? Do you already have a song on the sd-card? The manual shows how to play the demo song. If you don't have a song, have you got a signal source you can input to the DP006, in which case do the meters show any activity? If you could describe the exact steps you've taken, maybe with references to the steps in the manual for playing back songs, we could help pinpoint the problem.