External monitor problem

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.

 

help

still need help please

 

no mirror effact

Thanks for the reply Eddy...the answer is there is no mirror effect. Like when I open a PP for class, I will see the formatting palette for power point but not what I am working on until I go to slide show. Further, there will be no desktop icons or anything else showing on the external, only on my MBP screen.

Also, the desk-top display is an old one, I have switched twice now and the external only shows the original. And as stated before, if I try to use a front row slide show the only thing that shows on the external is the desk top image. So basically, unless I have a PP in slide show format the only thing that will show on the external is the formatting palette and an old desk top image.