Powerbook G4 not fully booting to login screen
If you have another Mac nearby with a FireWire port, you can likely book the PowerBook in Target Disk Mode. Power it down, then hold the T button when you turn it back on until a FireWire logo appears on screen. You can mount it as a drive on another Mac, and restore the files you altered from your backup.

If you don't have a backup, you could at least use Target Disk Mode to make a backup of your data so you won't lose it when you restore the PowerBook from its restore CD/DVD.