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Some dell models have synaptics control panel app that has that exact feature. To TURN OFF Touchpad when USB mouse is installed.
This solution applies to those who do not have a touchpad disable button on an F key at the top of your keyboard and have the Synaptics driver that does not show the option to disable the touchpad when the external device is present.
Here's a solution that may work.
1. Go to the Dell website and get the latest driver for your touchpad. Install it.
2. Once installed, go to c:\program files\synaptics\syntp in your windows explorer.
3. Open the program called DellTpad.exe (there is also one called DellTouchpad.exe -- don't use this one)
4. Once open, click Device Settings.
5. Now the checkbox is there at the bottom! Just click to make this active and it works like a charm.
Thanks for the above. I went thru the steps and got stuck on #3 as the delltpad application opened a window but there was nothing in it. I tried it twice and waited for 5 minutes and nothing came in the blank box on the screen.
I then opened the control panel/devices/mouses and saw there now was an option to "leave touchpad on when mouse connected". I turned that off and that fixed it. Evidently this is a newer driver then the one you explained, but it did the trick. Thanks so much. Bob Richards