Have you check to make sure that the video codec, the audio codec and the resolution are all supported as listed in the manual?
Often times, if these files haven't been ripped or encoded correctly, they may not work. Reencoding the files may be necessary for them to play on different devices.
I recently bought Samsung series 7 3D LED TV (UA46C7000WF). When I try to play mkv files through external usb hard drive, it doesn't play. Please help. Also, can someone tell me how to play external subtitles?