I've read that by using the web updater to get the latest firmware update will replace any corrupt or missing files except the map.(Latest maps available here, just pick which one, Navteq or sensis).
That's assuming you can connect it by usb to the internet.
I also found this on another forum;
Edit: you could also try the hard reset option as followsI contacted garmin and advised them I must have deleted some files when I was adding and deleting some photos and vehicles. They send the original files to download into the gps. This worked as it set my gps to new in the box condition and everything works great.
To hard-reset the unit. This has been known to clear up odd issues after a firmware update. This is one of the first things Garmin will have you do so be aware. They will also likely have you do it while on the phone with them even if you have already done it.
Hard Reset procedure:
This procedure has been known to delete your favorites so back them up beforehand: From the nuvi drive, copy x:/Garmin/current.gpx to your backup location. After the hard reset, copy current.gpx back to the same folder on the nuvi but rename it temp.gpx (important). On the next power cycle, the favorites will be read from temp.gpx into the non-user accessible memory area on the nuvi where they are actually stored (current.gpx is only a shadowed backup of your favorites)
Hard Reset:
*Note that this will clear all user selected settings on the unit
Power the unit off. Press and hold (and continue to hold) the bottom-right corner of the screen while powering the unit on. Continue to hold the screen until the "Do you want to erase all user data?" prompt appears. Press "yes" and the unit will reboot. Reset all your location settings and user preferences.
If possible after the hard reset, let the unit sit outdoors in the open for about 30 minutes or so to let the unit re-acquire the satellite almanac data.
Hope that helps.
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