You can try this:

If you have SD card,remove it from nuvi and try turn on nuvi or if you dont have SD add it in nuvi.

Connect nuvi on power in car.

Connect nuvi to pc and hold power button about 60 second

p.s.
When you disconnect battery you must whait about 5-10 min before you connect back.
I try this on old nuvi whit satellite problem with no signal,no satellite lock (205,660,350..) after 10 min when i connect battery back all nuvi lock satellite and work.