A master reset will erase all favorites1 and will restore your device to the default factory settings. If you would like to back up your favorites to your computer, you can find instructions to do so here.
To perform a master reset on a nuvi 200, 205, 405, 500, 600, 700, 705, 1100, 1200, 1300, 1400 series, 1690, 1695, 2300 LIVE series, zumo 220, 450, 550, 660, and 665:
Start with the device OFF and unplugged from power
Touch and hold the lower right corner of the screen with an index finger or the eraser end of a pencil
Continue touching and holding the lower right hand corner of the screen then power the device ON
Release the power button when the device powers ON
You will see a new message: "Do you really want to erase all user data?"
Remove your finger from the touch screen when this message displays
If text language is not in English, this is the button on the right
The device will now reset. Follow the on-screen prompts and then place your device in an area with a clear view of the sky until it acquires satellites.
Although the master reset will erase all saved favorites, any loaded custom points of interest will remain intact on the device.