This is the problem. With torrents you never know what you are getting.

You say these videos are not illegal, but I would have to question the wisdom of using torrents, and why not get those videos from elsewhere if they are not copyrighted or illegal copies.

It may be a codec issue. Have a look at GSpot Codec Information Appliance. It can test videos for both video codecs and audio codecs, and give you an idea if your computer is missing the proper codec for each video.

But if these videos are free, I would suggest you get them from elsewhere and not trust torrents.