not sure about the features of your devant. please check the audio format of your movies. chances are your tv cannot decode dts, dolby digital or ac3. to be sure, try to check using different movies with different audio formats. if other movies will have sound, then just download those kinds of audio format.
by the way, this is the wrong section to ask for help on this matter. it should be at forums -> home theater -> displays -> flat panels
good luck.