MacBook :: Plug In Headphones Or External Speakers Won't Get Sound

I have a problem with the headphone jack of my macbook. When i plug in some headphones or external speakers, it wont get sound to them, just like the headphone jack isn't there and the sound come out from the macbook speakers. The only ones that seem to work are the ipod original ones, but not if insert them completely, they need to be strategically plug in, like half in and half out, and if i move it a bit more the sound goes back to the speakers again. Does anyone knows what this might be and how to fix it? I can't use the warranty, because the warranty time already passed.