Basically i use both headphones and speakers on my mac and i have been having this problem. Sometimes no sound will be coming from the headphone jack and recently no sound from the speakers. However when i go in to preferences, sound, and then click on 'output' and then click 'internal speakers'...the sound then from the speakers then work again. Shouldn't this be automatic? Every-time i switch from headphones to speakers i have to go through system preferences and then click on 'built in speakers', if not, no sound comes. What should I do?