The phone supports aptX so it's hard to say what could be wrong.
If you get no sound from the phone while playing music that indicates that the phone is sending the audio to your headphones. Try restarting both the phone and headphones and see if that helps and also try updating your phone using a computer (http://www.sonymobile.com/global-en/software/computer-software/).
If you still don't get any sound i recommend that you try your phone with another headset or headphones to see where the problem is.
