I have hardware "volume up" and "volume down" on my Lenovo Thinkpad W530. They used to work to increase and decrease volume. A day or two ago, they stopped working. xev sees them, in settings>keyboard>shortcuts, they are correctly assigned, I can assign other key combinations to change volume and that works, I can also assign the hardware keys to different actions and that does not work. It works for a guest account. Reboot does not help. I am at a loss what might be causing it. Any ideas where to look for causes? This is on 14.04.
I had exactly the same symptoms with 14.04.
I imagined that VLC had 'grabbed' the media keys so I removed VLC. The problem persisted ...
I followed a reset suggestion that I found on the web:
Open a terminal and enter,
gsettings reset org.gnome.settings-daemon.plugins.media-keys volume-up gsettings reset org.gnome.settings-daemon.plugins.media-keys volume-mute gsettings reset org.gnome.settings-daemon.plugins.media-keys volume-down
This didn't seem to have any effect (which is why I closed the page and lost the link!). So I reinstalled VLC. But the next time I used an audio application I discovered that the media keys were working.
Maybe it was just luck and the keys will stop working again, but for now I'm a happy bunny :-)
Turns out this is a known bug.
keyboard>shortcuts>sound and media>
Then, redefine volume shortcuts (using those volume keys of your keyboard)