Unfortunately it sounds like it's failing. If you have something else to boot off of on the machine, such as another PPC Mac like your G4 via Target Disk Mode, do that. You'll at least be able to see if it's a software issue. Reset the PRAM for good measure, but it most likely won't help.

You might be able to repair it, but most likely you'll need to replace it. Keep in mind 12" Powerbooks aren't the most fun thing to work on.