Almost certain that the HD has breathed its last.
the blinking question mark means that the system cannot find a valid system folder from which to boot.
This can be caused by a few things;
The system folder contents have become corrupt for some reason
The hard drive is dead, even though you hear it spinning.
Boot the system from the installation DVD/CD and use Disk Utility to check the internal disk.
Just as a matter of interest, did you post in the Classic forum on purpose? Are you running System 9 on that G4 or OS X ?