If you press FN and F3 at the same time again the light above the touchpad will turn off meaning the touchpad is now enabled. This will allow you to enable or disable your touchpad. There is even an option to disable the touchpad only if an external mouse is attached. On my Dell Latitude E6430s, the option is POST Behavior > Mouse/Touchpad. In this instance, we want to enable or disable the touchpad if you notice on the F3 key there is a picture of a touchpad with an X through it. The touchpad can often be disabled in BIOS. The FN key allows you to use those orange icons.

It is located at the bottom left corner of the keyboard to the right of the CTRL (Control) key. NOTE: While this model is no longer sold by Micro Center or the manufacturer, this information may still be useful to those using this model of computer. This article will show you how to enable and disable the touchpad on a Dell Inspiron 15R Notebook. How to enable or disable the Touchpad on a Dell Inspiron 15R Notebook - Micro Center