Hello buddy!
Did you drop the phone somewhere or something ? Try to manage the phone profiles ( silent/discret/normal and etc.). Is the music plays normal ? Use your headset and call someone... is it works?
If nothing from above works try to factory reset the phone (the problem may be software):
1) Save your needed information (photos/videos/music and etc) on your computer.
2) Factory restart the phone with everything clear!
If the sound is still off get this phone to service.