There are three possible problems that are associated with an unresponsive touchscreen. They are listed from easiest to hardest to complete.
Dirty Screen:
* If your device has a screen protector, remove it
* Spray a bit of water or formulated spray onto a microfiber cloth.
* Wipe thoroughly.
* Using another dry microfiber cloth, immediately dry the surface.
* Replace the screen protector with a new one if desired.
Resetting the Device Without Using the Screen:
* With the GPS unit off, press the bottom right hand corner of the screen. Turn the unit on while maintaining pressure in the bottom right corner. When you see a prompt asking, "Do you really want to erase all user data?", you can release your finger and select yes.
* If the bottom right of the screen is unresponsive then please refer to the broken screen guide.
Broken Screen:
* If your device screen is still unresponsive after following the following guides above please refer to this guide for replacing a broken screen