Hello,
You do have an older Mac... thinking that it is not one of the trayless models of the newer era (ones that you slide the disk into a slot).
A Mac running pre X will not be able to use the CD-ROM with the extensions off... it is possible that you disabled the CD-ROM extension, and/or the support extensions (one was called High-Sierra, another was ISO 9660, and I think there were one or two other support extensions).
There are a couple things you can do.
* Turn the Mac on and hold down the C button and slide in the System CD-ROM before the computer starts loading. This should enable the computer to boot with the system CD, and it will test if your computer can read the disk or not. If you do not hear the disk spinning in the drive, then there is a hardware problem.
* When the disk is in there, and turning, do you hear a grinding / scraping noise? If so, we have an alignment problem.
You can also get into the OS, and look for the System Profiler application. If you cannot find it, go to the internet, and see if you can find some software called TechTool Pro. You might also search for other system-identification programs, and download them. I remember using TechTool Pro though.
Anyways, Check to see if the computer can find the CD-ROM. It will most likely be a SCSI device. If the computer doesn't find the CD-ROM, it will not know that it should use the device.
Let us know how it works for you.
Christian