Caps Lock green light will not turn off

THE GREEN LIGHT ON MY CAPS LOCK WILL NOT GO OFF. IF I TRY TO DEPRESS IT IT DOES THIS: 4rfv,4rfv,4rfv. IT ALSO REDUCES THE VOLUME ON MY SPEAKERS! IF I PRESS THE NUM LOCK KEY, HOWEVER I CAN TURN OFF THE GREEN LIGHT ON MY CAPS LOCK KEY. THE PROBLEM THEN IS THAT I CAN'T TYPE LETTERS! THIS WEIRD BEHAVIOUR SEEMS TO HAVE OCCURRED FOLLOWING THE CONNECTION OF MY G4 POWERBOOK TO A DATA PROJECTOR, ALTHOUGH THIS MAY NOT BE THE ROOT CAUSE. MY PROBLEM OCCURS WITH EVERY START UP, NOT JUST NOW AND AGAIN. I HAVE TRIED VERIFYING PERMISSIONS AND ALSO DONE A "SAFE" START UP, BUT THE PROBLEM IS STILL THERE. IT DOES NOT HOWEVER OCCUR WHEN I CONNECT MY MAC USB EXTERNAL KEYBOARD TO THE POWERBOOK. The only way I can type using lower case letters is by permanently having one finger on the caps lock key, which isn't very convenient. I DON'T THINK THE PROBLEM IS TO DO WITH THE KEYBOARD ITSELF - I.E. PHYSICAL DAMAGE, OTHERWISE, WHY SHOULD IT BE POSSIBLE TO GET THE CAPS LOCK TO REMAIN OFF ONLY WHEN THE NUM LOCK IS DEPRESSED? PLEASE HELP ME SOLVE THIS PROBLEM. CAN I FOR EXAMPLE, REINSTALL AN UPDATE? I'M CURRENTLY DOWNLOADING THE 10.5.7 DMG UPDATE BUT WILL I BE ABLE TO RUN IT, IF I HAVE ALREADY UPDATED MY OS? WILL DOING THIS SOLVE MY PROBLEM? IF NOT PLEASE TELL ME WHAT WILL? This hasn't solved the problem - typing this using another keyboard (bluetooth) perched on top of my PowerBook.