Everything looks good.
I think you have a Hardware Fault.
Have you tried to contact Garmin Support ?
Please delete your Garmindevice.xml from web also your unit id.
Another trick
copy this file to an SD Card in folder named garmin.
Express will then See your device and you will be able to update maps.
You might be able to use Running programs from SD on nuvi to copy files to Nuvi.
Some users survive this way.
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