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That sounds bothersome and severe.
How did you attempt to update it? were you updating the system software on the garmin device, or just the map(s)?
If you have not tried it already, updating it with Garmin Express sounds like an ideal approach to try.
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, by using the Reply To Expert function, how that approach goes, please. It's a chance that your Garmin device might be recoverable and work again.
Then unfortunately either the cable connecting it to the computer is bad - try a different cable, and/or try a different USB port and wait 2 minutes before restarting the Garmin Express program - or else the Garmin device is defective and will have to be either serviced by Garmin, or replaced.
How old is it?
And do you consider it worth the expense of service-repairing, if it is not within warranty (which would make the repair charges Free, of course...) ?