Have you done a basic reset (hold down power button down until it reboots), or done the factory reset? Did this happen after a new map download? If so, try to reinstall the map again.
How old is it? Is the internal battery holding a charge when unplugged? Is it possible the battery is giving out and your power attachment isn't making a strong connection hence you run out of juice? We have a 3590 as well. It doesn't do the rebooting problem but it is no longer holding a charge for use unplugged. We have to keep it plugged in all the time to use it. It is possible to replace the battery but that does involve opening the back.
Garmin nuvi 3590LM keeps rebooting
