Hi, Jeremy. Welcome to Apple Support Communities.
Can you tell exactly which model it is?
You can choose from this list:
http://www.everymac.com/systems/apple/ibook/index-ibook.html
Also, no iBook G4 can run Mac OS X 10.0.x, so it would be helpful if you can tell us which version of the OS is installed.
Do you have the system discs that came with the iBook when it was new? Do you have any other system install discs?
Are you able to start up in Safe Mode?
http://support.apple.com/kb/HT1455?viewlocale=en_US
If this works you will see the normal desktop Once completely started up in Safe Mode, try to restart normally and go to Applications > Utilities > Disk Utility. Click on the top hard drive icon in the left sidebar and note the S.M.A.R.T. status at the bottom right of the pane. What does it say?
Select the named boot volume in the left sidebar, ("Macintosh HD" unless it has been renamed). What is the hard drive capacity and how much space remains available on it? Repair permissions on it.
See if you are able to do a little hard drive maintenance to help things out.