I had the exact same thing happen to me when I had my Blackberry.
Unfortunately, there is no rhyme or reason as to why your sound profiles are no longer playing. Under certain conditions, ring tones, alerts, and media are not audible and no error message appears. These might work initially, but over time, become unresponsive. Symptoms of this condition are as follows: When playing an MP3 file, the media application closes with no error message When scrolling through sounds within the Profiles application, none of the notifiers make a sound When receiving an incoming call, the calling number and name is displayed but the ring tone does not make a sound Alerts from other applications (for example, instant messaging, alarm, or message alerts) do not make a sound Often times, a quick fix would be removing the battery for a few seconds, insert again and then try the sound profiles.