I have tried this method.
The flasning was not succesful, but after this pre boot mode is available again.

When I try to flash propper SW for Nuvi 610 with updater, the flashing process starts, but after some time it gives an error.
It is stil Nuvi 310 , SW V 5.20 in Webupdater.

When I turn on the device it starts loading, but after some time the display is white again.

Is there any solution for this situation?