Software :: MacBook Pro Not Recognizing DVDs

I own a MacBook Pro, around a year old, which is not recognising any video DVDs I insert. After putting them in, the computer makes the usual motions and sounds, but after a few seconds spits the disk out again. The disk isn't mounted on the desktop during this time, and DVD player does not launch automatically. I have tried opening DVD player myself while the computer is trying to find the disk, but there is still no result.

My MacBook has previously recognised these same disks, up to a few weeks ago when I found I might need to insert the disk two or three times before it played. CDs are still recognised by the computer (and iTunes, as well as mounting on the desktop), as are DVD-ROMs. I have tried many different DVDs, all of which play in my other Macs and DVD players.