I am trying to fix an iMac that is used strictly by teenagers (therein lies the problem). The iMac at first seemed to have symptoms of system file corruption and the problem widened as I tried to fix it. I am now at the point that I can't boot it in anyway. I have tried booting from various CDs while holding the C key. I have tried overriding the hard disk with the shift-option-apple-delete combination. I have done the option-apple-P-R to reset the PRAM. I have even opened it up and reset the little red button for 30 seconds. All I get on startup is the chime followed by a file folder with a flashing question mark alternating with the OS logo (the faces). It is a slot loading iMac - a few years old. The CD go in and come out fine and I can hear them spin up but nothing else. I don't know what to try anymore. I've never seen anything like this. If you have any ideas, please email me at susan@stedit.com or reply to this post. Thank-you for your time.

Did you try using the Restore CD that comes with your Imac?

I think you are SOL at this point, if you can't boot from a CD. Make sure your keyboard is connected to the imac also.

I have exactly the same problem. Tried to do a bios update 4.1.9 and that does not work as the hard disk is not recognised during boot. A system hardware check shows all is fine. If I boot into open firmware and type boot-mac it all works great, cd, hd, you name it, it boots but not from scratch.