A blocked CD is preventing your iMac G4 from booting properly:
- Restart the computer.
- Immediately after the startup sound, hold down the key combination (Apple-Option-O-F).
- Release the keys when a white screen displaying "Welcome to Open firmaware appears. (the keyboard will switch to Qwerty)
-type: eject cd
-Press Enter, wait a few seconds. The disc drive should eject the CD, and "Ok" appears on the screen
-Type: mac-boot (q and c keys) boot on a French keyboard)
Thanks to Sanspseudo for this tip.