irst of all thanks everyone because I have read how fast and clear your answers are. Im so sad because I can not hear anything on my computer (no music by itunes, no videos in youtube, even the sound that all mac users can hear when we start the computer)... I have put the headphones in the jack and also is impossible to hear something. I made the hardware test bye restarting the computer and pressing a long "D" and it said that everything is "working perfectly" on my macbook pro5,1 version 10.5.8. Also I went to system preferences>sounds>output> and I verified that the option of silence was not selected. Please help me, Im not in my country and I really dont know what can I do... Im afraid that something really bad is going wrong.. I hope you can HELP ME!