No Sound on MacBook Air

Try an NVRAM reset:

Reset NVRAM or PRAM on your Mac - Apple Support

johnathon288 Said:

"No Sound on MacBook Air: My sound doesnt work unless I shut down my Mac and turn it back on. Usually happens in the morning when I first go on my Mac. It gets really annoying to keep shutting it down to get sound!"

-------

Try Reseting the Core Audio:

Use the following command in Terminal (Found in System Preferences > Utilities):

sudo killall coreaudiod