Your HD is most likely gone.
Argueably, there is a chance that you can recover your info with utlities like VirtualLab, Norton, or TechTools, but in my experience, they prove fruitless.
You most likely will be able to intialize your disk and start with a clean one, though. Try pulling out the HD and sticking it in another Mac. If it still doesn't pop up, use Drive Setup under Utilities (OS9) to initialise and format the drive. Pop it back in and install the OS.