Volume keys not working

Hi all

The volume keys are not working when I press F10 or F11. It's irritating for me as I listen to a lot of music.

I have Macbook Air running OS X 10.9.2.

I attempted to fix the problem via this:

In the Keyboard screen of System Preferences, I ticked the check-box stating

"Use all F1, F2 etc. keys as standard function keys. When this option is selected, press the Fn key to use the special features printed on each key."

However, even after this my volume keys are not working.

Any help or suggestions welcomed.