I have seen this if the boat power is low or if someone powered off breakers without fully shutting down the unit. After ensuring good power, I would recommend trying a factory clear/reset of the display unit to see if that resolves the issue.
I have a similar issue except mine continues to go to the installation wizard and won't recognize anything on the network. I tried the master reset but did not resolve the issue. Is there a recovery disk similar to that of a computer? I work with a bunch of other people and I am pretty sure on numerous occasions the boat and furuno were not properly shut down which could have corrupted the software.