Yes, portion of the interior can go bad and the handle remain in the on position.
You can reset many by turning off all branch breakers then turn off main breaker applying light pressure toward off. Then turn the main breaker on, then each branch breaker one at a time.
Another item that could be suspect is the transfer switch. Verify that you have in deed lost incoming power to the main breaker by using a voltmeter. Turn off main and read each leg and across main breaker. Each leg to ground and neutral should read 120 volts plus or minus a couple volts. If shore power is correctly wired you should read 240 between the two legs.