Hello Linux Geeksters.
In this article I will show you a temporary fix for Xubuntu 13.04, Xubuntu 12.10 and Xubuntu 12.04.
When the mute button on the keyboard pressed, both the Alsa Master Channel and the PulseAudio Master Channel get muted and when you press it again, only the Alsa Master Channel gets unmuted and you get no sound.
$ amixer -D pulse set Master 1+ unmute
For an easier usage, alias this command to unmute:
$ alias unmute='amixer -D pulse set Master 1+ unmute'
To make this persistent, add this alias to your ~/.bashrc. When your computer stucks on mute, just type unmute in the terminal and things will get back to normal.