Good morning! My name is Alison. It would be my pleasure to help you with this.Generally speaking I would never advise that you disconnect until an update is completed, as it can corrupt your Nuvi, but....in this case, it is the only thing that you can do. It sounds as though the software download and/or install has been corrupted. Please disconnect the Nuvi from the computer. Try to power it off and then back on. If it freezes, won't starting or is generally misbehaving, we'll need to a master reset on the unit.
Please note: A master reset will erase all your waypoints or favourites and will restore your unit to the default factory settings.
To perform a Master Reset on your Garmin Nuvi 700 Series
Your device will automatically reset. Follow the on screen prompts then take your device outdoors to acquire satellites.
Please give this a try and let me know the results. Thank you!