I would be concerned too if there was no audio coming from my Mac. I recommend following the steps in the article listed below to troubleshoot issues with audio on your MacBook Air:
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hi, can you please help me I have the same problem,..
my audio on macbook air (mac OS X Lion 10.7.5) has recently not working. I can see the icon on the menu bar, but i cant increase the volume... it has a sign like the one on the "no smoking sign". I already check the system preference but its says that there was no input /output device. I also tried using my headphone, and still the same plus theres no light indicator. I'd search the net to check for the possible remedy, I tried the option+command+P+R but my macbook wont restart, the LCD sort to blink from blank to white. I also tried to used the repair permission disk, and even deleted the com.apple.bezelservices.list .. I dont know what to do. please help