I just installed LMDE on a brand new laptop. When I inserted a movie-dvd for the first time, it was loaded not causing any trouble. But since then, there seems to be no automatic mounting of dvds anymore.
Mouting the dvd manually works fine and even when I open a video player - vlc for example - the dvd gets loaded after a short while.
That wouldn't be too much of an issue for me, but since it's about a laptop of a friend of mine - who isn't too experienced when it comes to technical affairs - I'd better fix it for him.
The output of
fdisk -l looks alright too.
I know that's only a small amount of information, but I don't really know what's of further interest for you in order to be able to spot the bug.