Is your DVD drive configured to play Region-2 movies? It happened to me once. I played a Region 1 (US, CA) DVD which I imported from the US in my DVD drive. Then I decided to play a Region 3 (SE Asia) DVD, which it failed to play. Setting my DVD drive to region 3 fixed the problem, although the number of times you can change the DVD drive's region is limited to 5 changes.