Then you'll need a DVD playing app, like WinDVD or Microsoft's own Windows DVD Player app from the app store. Those who control the DVD and Bluray standards wants money for you to be able to play back the movies you've already paid for. Because that's how business works...
Edit: I just googled it, there is apparently a free DVD/Blu-ray player app called Leawo Blu-Ray Player. It's very basic but you at least get it for free.
Answer unselected since problem is not resolved yet. If you feel therealduckofdeath's answer was still appropriate, feel free to reselect it once the issue has been confirmed to have been solved. Personally, I think VLC will solve the issue.
Also, unlike what was posted previously, there is no licensing issue with DVDs like there is with Blu Ray movies. Only specific codecs are required to play DVD commercial movies, unlike Blu Ray which requires the software to be licensed, which costs money, which is why all of the Blu Ray software players EXCEPT for Leawo charge for the player. How Leawo is able to offer it, short of the fact that it has pop up advertisements, is beyond me, but who cares. I use it for Blu Ray playback currently as well.
This is not relevant to your situation as DVD playback has no such issues.