Does nuvi start normally? Does it work fine?
If yes probably Garmin support gave you the right info, it's probably a socket problem,it charges but a damaged pin might cause it doesn't connect USB into mass storage.
You can download from forum and load the new map and addition files to an sd and deselect the old one in internal memory or
better thing IMHO is to delete old files in internal memory using deleting commands loaded from an sd.
How to in this thread: [Only registered and activated users can see links. ]
I've a damaged socket pin nuvi and I update it this way.
PS. Try all the USB cable you have, sometimes it happens one of them might connect nuvi to pc even if a pin is a bit bent.