It's possible that if it's a new form of Windows that the Digital Rights Management is preventing these disc's from working. M$ added a more robust DRM Option to Vista and 7 than what XP had and this can cause DVDs to not play.
If you are using XP it doesn't natively support DVDs so you need a add in program that can play them like Nero's Showtime or Cyberlink DVD Player. If you are using the newest versions of these products it's also possible that the Security on the Disc is preventing the Disc from being played in a Computer to attempt to prevent Piracy.
If you're asking for technical help, please be sure to include all your system info, including operating system, model number, and any other specifics related to the problem. Also please exercise your best judgment when posting in the forums--revealing personal information such as your e-mail address, telephone number, and address is not recommended.
why won't my dvd play?