not sure if this is old news
i was having trouble trying to play (mkv files)
in media center . now i found out all i had to do was uninstall my (ati) video drivers
that i downloaded from ati and uninstall the code packs i already tryed. then reboot and open windows update. the new ati drivers are there. i downloaded them and then installed x64Components_v166.exe again . now media center plays all my file formats with no trouble. hope others find this usfull .