I understand, and it's a shame when devices won't work, suddenly, in this fashion.
I would advise you to download and install Garmin Express software onto your computer.
Then connect the Garmin Nuvi to the computer.
Then run Garmin Express, and update the Garmin device.
This may fix the Nuvi device's problem, if it is simply a matter of corrupted internal software on it.
When dealing with an update for your Garmin device, it is best to simply download, install, and use Garmin Express.
and (if you have a Windows PC) click on the big blue Download button at center bottom of the page. (If you have an Apple, click on the nearby Download for Mac link.) And download Garmin Express' installer to your computer, save it, then double-click upon it to install Garmin Express.
Then start the program, Garmin Express. Then connect your Garmin device. Then use Garmin Express to update your device.
Let me know how that goes, please. Thanks.