Amy, that is the exact symptom I had. You tube and iPod tunes work, but no game sound. Oh and earphones always work.
Check that the little slider switch next to the volume control. Red == mute.
Thanks a lot İ had the same problem and that little slider switch is the solution
When you choose mute in the setting that slider switch works as a sound mute
But when you choose lock smith this slider switch works as a lock for the screen