I wasn't aware that the unit froze on the welcome screen...
Try resetting the unit by holding on the power switch for 10 seconds or pressing the reset switch (if it has one)
Also try updating the unit software:
It is possible your firmware has got corrupted and this will correct it...
Go to this link and download the webupdater software, run the software and connect your GPS to the computer via a USB lead when prompted.
Not good news I'm afraid..
Sounds like the unit has some internal problem... You will need to call Garmin to organise an exchange/repair...
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