New (Blank) Hard Drive Installing OS 9

Hey there, I got an iMac G3 for my girlfriend and I'm trying to get it to work.
It has a hard drive that was wiped by it's previous owner and ultimately I want 10.3 on it. I boot up the computer and the flashing ? icon comes up so I put in the disc and when nothing happens I restart holding C. Still nothing happens.
I've tried resetting the PRAM and doing disk repairs and reformatting in disk utility but nothing seems to get it to work. I know the optical drive works so that's not the problem.
Any help is immensely appreciated!
Sean

I got another OS 9 cd and tried it with the same problem. No ideas as to what's going on?
For clarity sake, it's a slot loading 400 indigo one from 2000 with a cd drive.

Hello,
You might try cleaning the installation disc, checking the installation disc on another Mac, and, if you haven't, make sure that when you boot up with the cd that you press the "c" key as soon as you hear the chime, then let go when you see the spinning gear.

Thanks for the suggestions, I'll try cleaning it. I always hold the c key down right away, maybe I should be waiting a little before I press it. The only other Mac I have is an intel-based MacBook so I won't be able to try it on that but the person I got the second 9 disc from said it was used 5 months ago with no problems. Thanks again