You Nuvi is HWID 827 really!
As Caty say hardware problem took place probably...
I don't think it is hardware problem, this device only doesn't boot after I made firmware update. probably because low battery power during update cause crash even I keep it connect to PC via attached USB cable (try to keep power). As Catymag said "Nuvi at restart loading updates need a charged battery, so never update with a poor battery"