I had this problem with my BluRay. Even though the player is only one year old, it stopped playing some DVD's. It would just sit there loading forever. What you need to do is update the firmware (software) on your machine. It sounds intimidating but it was actually pretty easy to do. Just go to the web site for your player and check for firmware updates for your model. Click on the file and download it to your computer. You will need to probably need to burn this file to a cd that you will then put in your BluRay player to update the firmware. It pretty much runs the update itself, the only important thing to remember is to not interrupt this process. Apparently this can damage your player.
You could take the player back for a refund but I think that eventually you will run into this problem with any BluRay player. These machines are really just a specialized type of computer and are designed where it is expected that people will have to update the firmware from time to time.