Sound issues
the sound isn’t working for my MacBook Air. What do I do?
Had anything plugged into the Earphone port lately?
Have you done a PRAM reset, CMD+Option+p+r...
http://support.apple.com/kb/HT1379
In fact, do 3 in a row, takes a bit of time.
Intel-based Macs: Resetting the System Management Controller (SMC)...