Share your experience!
Hi! I have the latest software in my phone but all sounds are lost. Notifications, music and videos cannot be heard but when I use the headset, they work just fine. I would really appreciate if you can help me with this one. Thank you! 
Since when did it happen ?
Dial *#*#7878423#*#* in dial pad/ phone pad > service tests > stereo speaker
See if any sound comes out.
If not then unfortualtely it could be a hardware problem. In that case you will have to visit service center in order to get your phone examined.
But before going you may try software repairing your phone.
SUS ( Sony Update Service) ... download and install it on pc and follow the on-screen instructions
http://www.sonymobile.com/global-en/tools/update-service/
________________________________________________________________