If you have a Linux OS system and wanna use multimedia keys (i.e. raise volume, volume down, …) that aren’t working, you have either you kernel configuration is not well done or your system is not recognizing such keys on boot somehow.
This post is not the answer but you can try it for the second issue above. The problem is, maybe, with xmodmap. You should have installed it first. Also, xev program.
The xev program makes possible to see key events generated to kernel. Probably, your problem is because your kernel is not recognizing such events. You can use the following scripts to test and generate such codes.
xev | sed -n 's/^.*keycode *\([0-9]\+\).*$/keycode \1 = /p' | uniq
Press multimedia keys. For instance, Fn + RaiseVolume key if Fn is necessary. Most of the key boards use Fn key in combination with others to get special key features.
Close the window. And edit ~/.Xmodmap file by puting the code. For instance:
keycode 162 = XF86AudioPlay keycode 164 = XF86AudioStop keycode 160 = XF86AudioMute
I recommed you to look at here for detailed information.