Laptop screen blank but images show on projector

[riverpilot]

For a number of years I have given a lot of PPP with Office 2007 that is until today. Somebody asked me if I had used the "Presenters" facility in PP? As this is something I have never used, I decide to give it a go.
Prior to my "fiddling" when doing a presentation my slides appeared both on the laptop and the projector.
Having clicked on "Presenter" a display screen came up showing two icons of screens marked 1 & 2. I have no idea what I did, but now with the projector connected to the laptop my laptop screen goes blank and my desk top is now on the projector. If I disconnect the data cable at the laptop the screen remains blank for a second and then the images appear on the laptop screen. The projector goes blank.
How can I go back to what I had before??