Make sure that your computer has a sound card to play the audio. If you do have a sound card, the content that is being played probably uses a compression codec that is not installed on your computer. To make sure that you have all of the codecs that are currently supported, reinstall or upgrade Windows Media Player. To do so, visit the following Microsoft Web site:

Microsoft Download Centre .

This issue may also occur if there is not enough bandwidth to play both audio and video. You may receive sound even though the video is not present because audio requires less available bandwidth.