Before making cure.
Also try to hold power button down for a long time then release. (Sometimes coaches the Nuvi to boot)
Also try hold the power button for a long time and plug in USB Cable while holding button down then release
Long time = 30 seconds.
I've sometimes managed to get Computer to recognize Nuvi using these methods (limited success rate).
If these tricks do not help proceed to pre-boot mode and Garmincure3