Are you using pulseaudio or alsa only ?
Originally Posted by zorgoth
I wonder if it is some app.
wine can do that for example. it need exclusive access to the soundcard via alsa, that will block pulseaudio from doing anything (system sounds, volume controls have no effect, etc.). It should work again when wine is closed. some other applications have the same behaviour.
edit: same problem occurs on my f11 installation when using self build wine without the pulseaudio patch and savage2, a native linux game. both need exclusive access to the soundcard without pulse and volume settings have no effect for me until i close these apps.