I realize that this is a old question. Interestingly I had the same problem in my laptop which I purchased recently in KL. I tried to play a DVD disc that was burnt in India. Fortunately the solution was simple in my case. Malaysia where I purchased the laptop comes under Group 3 country for DVDs. So the DVD drive was configured during manufacture to read the DVD made in the same region 3. The Laptop allows to change the region a limited number of times only. So in my case I changed from region 3 to region 5. I had to close the player and re-open it. Bingo! The windows media player is playing the DVD now!
I have reproduced the region details of the DVDs below:
Standard DVDs
Region 1: U.S., U.S. Territories, Canada, and Bermuda
Region 2: Japan, Europe, South Africa, and the Middle East, including Egypt
Region 3: Southeast Asia, East Asia, including Hong Kong
Region 4: Australia, New Zealand, Pacific Islands, Central America, South America, and the Caribbean
Region 5: Eastern Europe, Baltic States, Russia, Central and South Asia, Indian subcontinent, Africa, North Korea, and Mongolia
Region 6: China
Sincere regards
Manickam