Will it play if you run the player and select the drive? It may be that the settings for automatically executing have been changed by an update. Letting things execute automatically when you insert a disk is not very secure. You can easily get a virus that way.
Have you tried a different DVD? When you view the DVD files in Windows Explorer, right click on one of the .VOB files and try "open with" and select either CyberlinkDVD or Media Player.
Will it play if you run the player and select the drive? It may be that the settings for automatically executing have been changed by an update. Letting things execute automatically when you insert a disk is not very secure. You can easily get a virus that way.