It's a Codec Issue
You could try a different Media Player. VLC Media Player has Codecs Built in and is Highly recommended here on the Forums. If you want to keep the Media Player that you are using then download only ONE Codec Pac as more than ONE may cause Problems. See the Link Below that LOTR put together for several solutions that may help.
CODECs list for Movies/Alternate players / Video help forums/ video-mp3 fixers
Also Always use Bitzi when downloading Video Files. Instructions below.
This is how it works. After you have completed your search, Right click on the file that you're interested in. Now go to Advanced > Lookup File With Bitzi. Left click on that and a new browser window will open which is Bitzi. Now you will see how other members have rated this file. If you see something like "Bitprint not found" then Leave it alone. Its probably a Fake or Corrupt File. If it has been Rated then you can read what or how the members feel about the file.
Hope this Helps.