should iBook boot without internal optical drive?

The iBook G4 12" and 14" should boot without an optical drive installed. They should also boot without an optical drive AND without a hard drive installed from an external FireWIre volume or NetBoot volume. If it is not booting from the hard drive or an external source after you extracted the optical drive, then you either damaged another component in the process or reinstalled another component or reconnected a cable incorrectly. If you haven't tried to boot from an external volume, try that. You should also make sure that the RAM is seated correctly and that the DC-in cable is connected to the underside of the logic board correctly.

All iBooks very much prone to logic board failure, especially the if the computer is handled incorrectly or roughly while disassembled. If that were the case, you computer would power on, but display no video on the screen f through the VGA port. If it doesn't power on, at a check the power connections. Do not cut any corners by leaving out what appear to be redundant screws. Screws do double-duty work in iBooks and the machine only coheres properly when they are all in the right location.