I don't know if this will help or not, but I also have both of the programs you mentioned and some of my dvd movies also won't play with Media Player...but I did get them to work with Power DVD once I downloaded the free codecs from http://www.divx.com and installed them.
Once I tested PowerDVD to make sure I could view the movies through that program, I went into the File Types and edited the Play with PowerDVD to be the default viewer instead of Media Player.
Hope this helps.....
My media player (version 10) wont play DVD's It will play avi. files and my MP3's with no problems but when I put in a DVD I get an error message and it says that Media Player has encountered a problem and needs to shut down. My other media player Power DVD does the same thing. What is the problem here? I did just update to the SP2 install. Could this be a problem? What should I do to try to fix it? And yes I do have a DVD drive