Okay, I don't use Mepis, but I'll see if I can help. How familiar are you with the command line?
First you'll need to make sure your user is in the audio group. Then you'll need to make sure that your user has access to the cd and dvd drives so that your user is allowed to use them.
Run this as root
gpasswd -a <user name> audio
and this as your user
and see if you have "user" as one of your options for your CD and DVD devices.
Thats a good start, see if it helps.