Macbook Volume Control Not Working
This happens to me all the time.  I often switch audio device's for pro audio, but it also happens other times using different applications.


Open Terminal (Utilities)
Enter "killall coreaudiod"
Enter your user/admin password


Your volume controls should be working now.  I've reset my NVRAM and PRAM, as well as repaired disk permissions, yet still have to do this quite often.

** Running this command while playing audio/visual via web browser has caused the command not to work and/or the browser crashing, most of the time it doesn't though.