Basically when you turn your computer on, the first black screen you are greeted with (Usually has Memory information and Processor Speeds etc) is what's called the POST (Power On Self Test). When you see this there should be some options on the screen saying (for example) "Press F1 for setup" or "DEL for BIOS". Basically follow those instructions and get yourself into the "Setup/BIOS" The BIOS is basically where you can set some pretty critical system settings, also has things like CD and HardDrive detection. There are quite a few different types of BIOS so I can't really be very specific with the one you have. You need to look for something like "Basic Settings" usually the first on the list of menu options. In there you should see your disk drives listed with additional information. If your two CD drives are not listed here then there is a problem with the way they are wired up, I would check with the manuals that came with them to see whether they are set to slave/master correctly.
If you are having trouble getting into the BIOS, if you're quick you can view the drives connected to your computer when POST is running.
Let me know how you get on
T