Why doesn't DVD Playback work?
There are several reasons why DVD playback may not work.
The first thing you should do is check that you are actually in DVD Mode. Zoom Player has two distinct playback modes, DVD and Media modes. You can switch between the modes either by pressing F10 on the keyboard, or by using the right-click Context Menu.
After making sure you are in DVD Mode, you need to make sure your system contains properly registered DirectShow DVD Audio and Video decoder components (filters).