My G4 freezes when changing start disk to classic mode at Welcome screen OS 9.2. I can't boot from any CD's because keyboard won't take commands. Previously the G4 functioned fine in OS 10.3 mode.

It would be nice to have a fuller description of the issue. Let me see if I can help. Try holding the "option" key down while booting the machine. This should bring up a blue screen with all available volumes you can boot from. If you can get back into either OS I would recommend connecting to the internet and running software update for both versions. The latest of each is OS 9.2.2 and OS X 10.3.9 as free downloads from that avenue. Assuming you do this and are still having problems. I would try to boot into either OS and backup your personal data to either an external hard drive or CDs/DVDs then reinstalling the OS. You can erase the entire hard drive and just put the software back on there. One other thing to try is that I have seen RAM cause this type of problem before. If you have more than one RAM chip in your machine try taking one out then trying to boot. Shut down, swap out the RAM and try booting again to see if one of the chips is causing problems. Good luck!