I have a similar issue on Ubuntu 14.04: for some reason Gnome-MPlayer, VLC won't recognize DVDs. I solved it by selecting a different CD device in VLC prefs. All these programs defaulted to `/dev/dvd`, but then complained. I changed the `Disc device` to `/dev/sr0` in VLC, and now I can easily play DVDs. If you use VLC, then try `Media > Open Disc > Disc Device` then experiment with the proposed devices in that list (or put in `/dev/sr0`). Does this help?

I have a similar issue on Ubuntu 14.04: for some reason Gnome-MPlayer, VLC won't recognize DVDs. I solved it by selecting a different CD device in VLC prefs. All these programs defaulted to `/dev/dvd`, but then complained. I changed the `Disc device` to `/dev/sr0` in VLC, and now I can easily play DVDs. Does this help?