Try the standard PPC “fixing” techniques:

– can you boot holding down the option key?
– can you boot holding down the shift key?
– reset the Open Firmware: boot holding down command-option-o-f and then type “reset-nvram” (return) and “reset-all” (return).
– zap the PRAM: boot holding down command-option-p-r until you hear the second chime.
– reset the Power Management Unit: I forget how this works on this model. Google “iBook G4 PMU” or “iBook G4 CUDA”.