Headphones port will not turn on


hello from sunny Spain.
Have a problem with a PowerBook 15" 800 mGZ . Some how I have
turned off the sound on my headphones port. Have checked the system panel sound panel, and the function keys. Everything is OK there when I remove the mini jack sound comes on the PowerBook speakers.I :mad: have had this problem once before but for the life of me can not remember the fix. Something not connected to sound ??? :confused: :confused: