You can try resetting the Nuvi:
With the unit turned OFF, hold your right thumb on the Upper, Left part of the screen and plug the USB plug from your computer into the back of your GPS. The unit should boot up and stop at the screen where it shows a little computer, wire, and little GPS. Your computer should now show the GPS as connected. Only now you can pull your thumb from the screen.You can then use Webupdater to install the latest updates again.
Let me know if that works ok for you?