I run Ubuntu 14.04 on a Sony Vaio CS series laptop. Normally, the volume is controlled by pressing Funcion+F2, F3, and F4 for mute, volume down, and volume up respectively. I accidentally reassigned the volume up keyboard shortcut to a different key. I tried resetting the keyboard shortcut by going into the keyboard shortcuts editor in Ubuntu and pressing Function+F4, but that didn't work. My mute function and my volume down functions both work flawlessly, but volume up doesn't work at all. Please don't answer telling me to change the keyboard shortcut in the Keyboard Shortcuts manager, as I have already tried that. Thanks for your help!