Not sure if you can do a factory reboot, if you can do that and see if that helps
if not, it may be time to buy a newer one
Perform A Master Reset on a BMW Motorrad Navigator IV
Note: A master reset will erase your saved information and restore the device to the default factory settings. This will include all saved locations, trips, and tracks. Any loaded custom points of interest will remain intact on the device. You can back up your saved information to your computer. See Backing up, Restoring, or Transferring Saved Data on Garmin Automotive Devices for instructions.
To perform a master reset on a BMW Motorrad Navigator IV device:
Start with the device off and unplugged from power
Touch and hold the lower right-hand corner of the display portion of the touchscreen
Power on the device while continuing to hold the display
Remove your finger when the screen displays "Do you really want to erase all user data"
Touch Yes
The device will automatically reset. Follow the on-screen prompts to set your locale and then place your device in an area with a clear view of the sky until it acquires satellites.