Perform a hard reset:
To perform a master reset on a nuvi 3400, 3500, or 3700 series device, hold the device horizontally and follow the steps below:
Note: 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 you can find instructions to do so here.
1.Start with the device turned off and unplugged from power◦To verify the device is powered off and not in standby mode, press and hold down the power button until prompted to turn off the device
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2.Power on the device
3.When the first copyright screen appears press and hold the lower right hand corner of the display portion of the touchscreen
4.Remove your finger from the touchscreen when "Erase all user data?" appears
5.Touch Yes◦If text language is not in English, this is the button on the right
The device will now be reset. Follow the on-screen prompts then place the device in an area with a clear view of the sky until it acquires satellites.
1Although the master reset will erase all saved favorites, any loaded custom points of interest will remain intact on the device.