Greetings...I have a Macbook Pro with 17" monitor that I use in my middle school class daily. I have it connected to an external monitor and had no problems until a student fooled with it when I hasn't looking. Now only Power Point works on the external monitor, I am not able to use the iphoto as a slide show any more, nor can I use streaming video. While both show fine on my computer the external monitor only shows my screen saver. Can anyone help me solve this problem, I would sure appreciate it.