fili - That means your hard drive is not mounting.
You will need to get it back using something like Disk Warrior. Disk First Aid (see your menus on your install CD) would be your first try but it rarely does anything. DW is a godsend.
You may have experienced a problem I encountered on my G4 the day I bought it and also a on a client's G4. The bootup would proceed normally but never get past the splash screen. The problem is the "Volume Wrapper " was damaged. DW fixes this easily. The Volume Wrapper is used on HFS+ disks so that if mounted in an older system that message about "can't see your HD?..." is shown. When it is damaged the bootup never gets to the harddrive.
Having said all that there are other reasons Hard Drives don't mount and you need a repair utility like Disk Warrior or TechTools to fix them. DO NOT use Nortons, it has ruined 2 of my drives and others on the forums have repeated the experience.
For some reason I don't understand some older FW drives are not available for installation either.