PowerBook start-up not accepting user password


When starting up my PowerBook running OS10.3.9, I'm asked for a user
password. After about 3 months of always accepting the password and
continuing on with the start-up, the password is now NOT being accepted and therefore the start-up is stalled at that password screen. No new software has been added recently that I can think of. Any help out there as to why a user password would change, or more critically, what I can do to get my PowerBook to complete its start-up?
For the future: it's pretty helpful to have an additional computer-admin account. Not only for such cases but also for troubleshooting many problems which are related to the settings.
And welcome to the forum.