DRUSS , open "my computer" and right click on your DVD drive. Choose properties and then click on the "autoplay" tab. In the drop down box choose the content type....eg video files , then tick the box "select an action to perform". Highlight "play using Win DVD" and click apply > OK.
DRUSS , I've no doubt you did , but as these type of applications tend to take over every aspect of your media files i think the first place we tend to look is inside the settings of the programme itself. Done it myself many times.