When the computer powers it, it alternates between a "folder with a Mac Face" and a "folder with a question mark"... indicating it cannot find a bootable operating system. 

I will include the Power Mac G4 Software and Install CD so you can troubleshoot and diagnose the issue - I didn't have time to go through all the troubleshooting steps for fixing or replacing what is likely a hard drive issues (either a corrupt install or the hard drive has failed)