When trying to play dvd wont due to saying either unknown disc or defective disc

Hey,
As i don't know the model of your dvd player or the type of dvd you are using I can only give you a very basic response for possible issues.  1. you are using a "burned" dvd on an older dvd player. Some older dvd players can't read dvd's burned from a computer. 2. The lense is dirty, scratched or damaged.. if other disks work in the dvd player, than this option is out the window. 3. DVD is damaged or defective. Just like the previous solution, if the disk works in other dvd players, this option is out the window 4. The DVD is from a different Region. Here in Canada and the US we are region 1, if you get a disk from Europe or japan. they are region 2 dvd's and thus don't work in our north american machines. 5. Some older DVD players have difficulty reading dual layer discs - just a though
I hope those were helpful, if not message me back with the dvd player model number and the movie or type of disk you were using.