@tomtompt.
Follow this [Only registered and activated users can see links. ].
step by step, read with care and then post results.
This is the only way to recover your nuvi.
After cure you must flash original fw or nuvi wont start.
As back up I meant a working set of files saved from an healthy nuvi, it's clear that if you copy files from a bricked nuvi it wont start at all.
So repeat the cure procedure and see if a garmindevice.xml will appear in Garmin folder.