iMac keeps ejecting CD

I was given a iMac 600 Mhz, blue dalmatian, which works well except that I can't boot from the CD-RW drive. The drive works perfectly except that it ejects the CD on start-up.
I have tried several boot-able CDs with the same result. I have tried: holding down the "C" key, holding down: Command, Option, Shift, and Delete, and selecting the CD as the start-up disk from the control panel.
On a PC there is a way to select boot from CD. Is there a similar option on this iMac. It is running OS 9.2.2.
I have used many Macs over the years. This is the only one that won't boot from a CD.
Thanks

Welcome to Mac-Forums, MAC3XX.

To boot from a CD, you can't use any Apple CD that is lying around: if you don't have the disks that came with the iMac, you need a full OS install disk, either an OS 9 or OS X disk.

If you take a CD that comes with another Mac, it is model-specific and will not work on any other Mac model than the one it shipped with.

I'm trying to boot from Norton's 6.0, Tech Tool Pro, Disk Warrior, and even a OS 9.1 install disk. They have always worked in the past on many different Macs. But they won't work on this iMac.
Every CD is ejected when the computer restarts.

The CD-ROM could be dirty then?