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.....