Sound doesn't work anymore with Yosemite Today, suddenly, my MacBook Pro is gone mute. The speaker icon on the top bar is faded gray and within the output devices there is not the option internal speaker anymore but just digital output and two Soundflower options. I've tried what was suggested in the thread
Sound not working when running OS 10 Yosemite but it didn't worked. When I restart my Mac, it makes the opening sound and it works with headphones.

What should I do to restore the sounds?
I had the same problem after upgrading to Yosemite and I've been looking for an answer on StackOverflow since. I found an answer which was not upvoted so it was harder to find unfortunately but here is a way which solved my problem:

Open your terminal on your Mac and type in:

sudo killall coreaudiod 

Press enter and you're done. It should work now.

PS: I'm re-posting this from my previous and exact answer to another user's same problem.

Hope this helps