We're not asking you to change anything. Simply look into the boot order to see if the CD drive is listed.
as Denholm posted , you are just looking
if it is not listed along with your other Hard Drives, CD /DVD rom devices, Floppy Drive , etc.....
then you can go to each channel and click on the auto/auto device recognize-find key ( this is named differently for different motherboards )
if it does not find it, it might be possible that your IDE ribbon cable has become broken inside it ( a common thing that happens with old IDE ribbon cables ) short of that.... the IDE Channel it is on may be going faulty on you......
just some suggestions........ best of luck to ya