This behavior is caused by a conflict between the clock in your PowerBook and an extension associated with Claris Organizer software.
Interruption of backup battery power can cause the clock to be reset, setting the year to 1904. If you have installed Claris Organizer (which comes with the PowerBook 3400), part of the installation includes an extension named Instant Organizer. As the computer starts up, the Instant Organizer extension attempts to reconcile your appointments with the "current date" of 1904. This results in the behavior you describe.
To resolve this, force quit by simultaneously pressing the command-option-escape keys when the described behavior happens. The PowerBook will then continue starting up to the Finder. Once the startup process is complete, reset the clock to the correct time and date; the computer will start up normally.
Note: If you force quit Instant Organizer, you must restart the computer before trying to use it or before launching Claris Organizer.