Flashing question mark

[Jude]

Hi all

A friend of mine has a G4 (? silver and grey)  that will no longer 
boot. It comes up with the flashing question mark on a folder which 
we know means that it can't find the startup system.

She thinks it may have been OS 9. She has flashed the PRAM but it 
still refused to boot.

It will not boot from any system CD. She has tried Norton Utilities 
without success.

Anyone got any ideas? Or can anyone point in the direction of a way 
of recovering this machine?

thanks

Jude