I think that maybe you have a corrupt file in your nuvi as kunix already posted.
If you flash GarminCure 3 in Cure Mode can you access the filesystem ?
If you can, then Backup the entire Filesystem including the hidden /.System folder
Once the backup is complete try deleting all files or formatting with rmprepusb as shown in the GarminCure 3 thread.
Then flash nuvi with GarminCure3 in original mode and try accessing Nuvi with PC (without putting back files)
Nuvi 1xxx can boot without files.