It's either a wrong type of disc or your player needs an update ! Is it a new movie ? Sometimes new movies won't play unless the player gets updated . If you have a laptop , then you can plug it in to the player , give it all the numbers it wants and it will update . Or you can have a Tech come over and do it in about 10 minutes !
This is an indication that the DVD is has some problem like scratches. This is because some DVD players will not detect the disk or fail to accept if it has risk factors. You need to try other DVDs and if they also don't play, you will have to take the player to a technician.