BIOS doesn't show CD-ROM IDE device

I'm doing computer support tech for a friend, but the situation is not ideal because (1) I am not local (doing it all over the phone) and (2) I don't know the model of his motherboard or really any other component in his system (he is going to open the case tomorrow and I may know more). But perhaps my issue is fairly straightforward. My issue is this:

The computer has two hard drives, one CD-ROM drive, and one DVD-ROM drive. The two optical drives are on the same IDE cable (master and slave), I believe. The goal is to boot from a CD-R.

First, when I tried to get him to boot from a CD-ROM, I asked him to press F8 for the boot device menu, and it only showed 3 devices: a floppy disk, and the two hard drives. It did not show either optical drive.

Second, when I asked him to enter the bios setup, the first page that shows all the IDE devices showed only the hard drives and indicated the other two IDE slots had no device present.

Any ideas how to debug this?