Rev.A iMac won't boot

I'm a relatively new Mac user, and I've just acquired, from a rubbish pile, an iMac rev. A (at least, by the manufacturing date, that's what I think it is ). I don't have any USB keyboards or mice, but I powered it up and it couldn't find any disc to start from. I put in a MacOS 9 boot disc that I'd made for my 4400, but it wouldn't start off that either - do I have to hold down the C key to make it boot from a CD even if it can't find any other boot media? I then dismantled it and swapped the old HD out for the Apple 2GB drive that I used to have in my 4400, with OS 9 installed. While I had the logic board out, I pressed the Cuda switch just in case it was a PRAM problem. I booted it up on that disc, but it still couldn't find a boot volume, and the disc kept on making a repeated seeking noise. I haven't tested the 4GB drive out of it in another machine yet, but are there any obvious solutions to this problem? I could scrounge a USB keyboard and mouse without too much trouble, but I don't want to spend much money on it - any ideas?