You may not have the required codec installed on your PC. Check to see if you are able to play the video files on your PC. If not then download and install the basic version of the video player with the relevant codec such as Quicktime Pro, RealPlayer or DivX player from the Internet. This will install the required codec on your PC. Make sure that you can play the file on your PC then try transcoding the file again with the Arcsoft Media Converter.