My iMac says it can’t find a CD burner or no software, but I have a burner listed under about this mac under CD burner.
Which application or action triggers the error message?
My first suggestion would be to quit iTunes and open it again as on occasion it just "takes over" the optical drive in the background and doesn't allow anything else to access it.
Deleting the system preferences file could solve the problem (see ha14 post), you might also want to open up the Disk Utility and repair permissions on your hard drive.
Deleting the System Preference or other .plist file