What actually will it do? Consider doing a PMU and PRAM reset as well as a safe boot.
If you received the operating system installer discs which the computer originally came with, that would be a place to start; could be if you just got the computer, it was set up for a Guest User or 'custom lesser-status user settings' some of them do not allow a lower-status booted user to change any settings at all.
The OS X could be set-up to require an Admin User account to check or change any settings, depending on if this is what is going on in there; and if the former owner or admin user had that iBook G4 set to start in a lesser-priviledged account, you may be locked out of the higher command structure, if that is so...
...a previous user account issue could be the cause of the problem you face. Without knowing more about the situation with more detail, probable answers would be more guesswork than science. There in: Parental Controls, Accounts/Users, and some other places, are where chosen settings can affect all non-admin activities.
With the correct and complete bootable installer disc set you could consider several things; to include clear the hard drive and reinstall a new OS. Then check for any/all available update/downloads.
So much of what goes on behind the magic unix curtain is like \/ ( ) ( ) | ) ( ) ( )
Hopefully this issue is a simple matter of account permissions or user priviledges.
Good luck & happy computing!