Any chance you "cloned" your system to an external hard drive that you can boot up off of?
When you purchased your G4, did you have the Apple Protection Plan. I'm sure it has expired, but you may have a disc containing the program "Tech Tool Pro". If you have that, try booting up off the CD/DVD and running this program.
It is quite some time since I bought it and it was a refurbed one. I'll look for that disc I may have it.
I don't use the G4 for much else besides the internet these days but it has some files on it I need. I used to run Cubase on it in OS 9 and have two partitioned HDs so I could boot in OS 9 or X when I needed to. ( I do my work on a macpro)
I have over the years had to repair and re-install the G4 system a few times but never had it crash while installing.
I think techtool is on the other drive but I can't seem to get it to a stage where I can choose which volume to boot from.
It goes into what looks like DOS, ie text with a promt and asks for a password. The only password I have is my administrators pw which doesn't work.
When I get back to it I'll post everything it the text says which I can't recall now.