VLC Media Player.
It can be downloaded from its official page here:
http://www.videolan.org/vlc/
If it doesn't work (either there's no sound or video or both), then it means that you don't have the required codec installed on your computer to read the DVD. Download one from here (K-Lite Codec Pack):
http://www.filehippo.com/download_klite_codec_pack/
It's free as well.