"Disc Cannot Be Read" Message Appears When Putting in a Disc

First and foremost, consult your DVD player manual and make sure the disk you are trying to run is supported by the player. The troubleshooting page has a list of supported disks. If it is, check the condition of the disk. If it is dirty, you can try to gingerly wipe it off with a soft cloth and try again. If it is heavily scratched, you might need to replace the disk. Download the product manual for instructions on how to clean your disk. If your DVD disk is clean, serviceable, and supported, you may have to look at your optical drive.