Hello becrjs,
Thanks for using the Apple Support Communities. We understand that you're having issue using an external DVD player with your MacBook. There are a couple actions to try and help sort out this issue. First, have you tried restarting your MacBook or booting up into Safe Mode to see if it's detected? If not, please start there.
Log out, sleep, restart or shut down your Mac
Start up your Mac in safe mode
If you continue to experience issues, go ahead and try a SMC and NVRAM reset, to see if that helps.
How to reset the SMC of your Mac
Reset NVRAM or PRAM on your Mac
Keep us posted on how it goes.
Best wishes.