If you have hooked up more than one CD/DVD and neither was recognized by Ubuntu, never put a CD drive and a burner on the same IDE cable, if it is possible to do otherwise.
There are several reasons:
- On old burners it caused a buffer underun error when you opened the CD tray while burning with th other drive.
- If both drives are positioned on a different IDE cable the OS can (but will only in an emergency) read and write at the same time.
In any case, if you cannot put a them in different IDE cables, set the burner as master and the reader as slave. The master MUST be at the end of the cable and the slave on the second place.