You are not successfuly flashing the device.
The Nuvi should restart by itself.
If you are installing Garmincure3 in Cure mode the Nuvi will not be bootable but will allow you access to the internal flashdisk.
This is to allow you to delete corrupt files and / or to format the Nuvi Internal Flash Disk with RMPREPUSB.
If you are installing GarminCure3 in Original mode the Nuvi will be bootable.

Please read this thread [Only registered and activated users can see links. ]