ok, it is one of two things, either the internal memory has failed (most likely based on the symptoms) or a complete failure of the firmware
To confirm this, you need to connect it to a computer you can install software on
Then install Garmin Express from my link below
Then run it, connect the garmin to the computer and if it says to perform an update allow it then see if it works.
If it does not say this or gives an error then you know the internal memory has failed
In this event, you are going to have to return the unit to have it replaced. It will be covered by the warranty if this has not expired, and the replacement will be done at no cost to you.
If you would like any additional information or assistance, please do not hesitate to let me know.
And if you can take a second to rate my service by clicking one of the stars at the top of the page, then submit, that would be greatly appreciated.