'log-in?' lock-out!

I run a G4 1.25 dual optical with 2gb of memory, using OS 9.2 (ludite tendencies i'm afraid!) working mainly in Illustrator and Photoshop, after nearly five years of problem free use, I can't get past my 'logging in' as soon as the password is entered and ok'd I get a bomb panel stating 'an error type 10 has occured' with the log-on application, I press 'restart' and the same happens again and again!
any suggestions?

1) Disconnect any peripherials except monitor, mouse and keyboard.
2) Try to ZAP your PRAM: command-option-p-r. It must make the "Chime" sound _3_ times before letting go.

Tell us how that works out?