I need help watching my laptop through my flat screen.

I know we have the audio and video cables hooked up correctly and in the right places, the problem we are having is switching monitors from the laptop screen to the television. When we use the fn+f4 function it switches the picture but the only way to switch it back to the laptop is to hard boot it. According to the fellow at the Geek Squad (who wants to charge me $200 to come out and look at it), the problem is probably with a setting on the laptop. Any ideas on what that setting might be and how to fix it? Any help is greatly appreciated!