A great alternative method If you cant access your BIOS or have a different problem is a program called AutoHotkey which can be downloaded at http://www.autohotkey.com/ . AutoHotkey is a great program that uses very little background processes and it's FREE!
Step 1: Download and install Autohotkey
Step 2: Run AutoHotkey then right-click your desktop and click "New" then click "AutoHotkey Script"
Step 3: Right-click the file you just created on your desktop and click "Edit Script"
Step 4: Start a new line beneath the line that says "SetWorkingDir %A_ScriptDir% ; Ensures a consistent starting directory." It should look like this http://i.imgur.com/hPzpTkr.png
Step 5: On my PC if I want to turn up the volume I have to press fn+f12 but if I just wanted to press f12 to turn up the volume I would type f12::Volume_Up on the first empty line. It should look like this http://i.imgur.com/gzQczHZ.png
Step 6: To do this for the volume down key and mute key you need to start a new line for each new key shortcut. It should look like this http://i.imgur.com/hizJxKU.png
Step 7: To run the script you just created you simply double-click it. You can put this script anywhere, I placed mine in a scripts folder I created in my documents.
Step 8: To make the script you just created run when you log in you will need to place it in your Startup folder. To do this on Windows 8 open run and type "%AppData%" (without the quotes) and click "ok". It should look like this http://i.imgur.com/hJbTUTv.png Then click the "Microsoft" folder, then click the "Windows" folder, then click the "start Menu" folder, then click the "Programs", then click the "Startup" folder. Once your in the "Startup" folder it should look like this http://i.imgur.com/XCscihU.png
Step 9: Make sure you saved your script in a folder where you want it (I would recommend not leaving it on your desktop before creating a shortcut). Now right-click the script and select "Create Shortcut". Then place the shortcut it creates into your "Startup" folder. Once your done with that it should look like this http://i.imgur.com/XCscihU.png
You can use this same method to make other unused keys do things liek play/pause media, play next track, ect... Here's a list of other commands http://www.autohotkey.com/docs/KeyList.htm
Use this formula for play/pause, next track, ect.. (key you want to trigger action)::(Action) = f12::Volume_Up