Hello BigAl-Manchester,
Welcome to Apple Support Communities. It looks like you're having issues with your External CD drive being unrecognized by your Mac. We'd be happy to look into this with you.
First, open up the "Finder" then at the top menu next to the Apple logo, go to: Finder > Preferences, and make sure "CDs, DVDs, and iPods" has a check mark.
Also, "External Disks", and "Hard Disks" are selected.
Next, try your external CD drive with another computer to see if it is an issue with the Mac or the CD player.
And finally, try the Disk Utility to check if it is recognized by your Mac. Here's how:
Disk Utility User Guide
Also, check out these helpful links:
How to connect the Apple USB SuperDrive
If you don’t see a CD, DVD, or Blu-ray drive on Mac
We hope this information is useful. Kind regards.