Well this extremely annoying stupid thig happened to me today, so i decided to make a post about it to help others who might be 
experiencing the same thing.
Well what happened was that i was listening to songs on my apple white macbook while working online and then i decided to plugin my headphones/hands free, and to my surprise i wasn’t able to hear any sound with the head phones! i tried testing taking out the hands free and again plugging it in, but it didn’t work.
I decided to restart my system to check the issue, but suddenly got something into my mind! and yeah! that was the issue causing no sound from the speakers! :D
Well, the thing was, although my macbook wasn’t mute on its builtin speakers, but once i put it on hands free, the laptop volume went to mute! I was on macbook with snow leopard 10.6 and missed the icon to see that the volume is on mute!
So the solution? well its pretty much simple! just unmute your macbook audio once you plugin the handsfree jack :)