locked volume

I tried resetting PRAM (did not work for me). Then I found someone had reset SMC. And this worked for me.

Reset SMC. http://support.apple.com/kb/HT3964

Choose the method for:

"Resetting SMC on portables with a battery you should not remove on your own".

Try This

https://discussions.apple.com/thread/3405419?answerId=25633972022#25633972022

it solved my issue... and then give me some points 🙂