Get Automatic Codec Updates
1.

Start up Windows Media Player. Click on the 'Start' button, choose 'My Programs' and then 'Windows Media Player.'
2.

Choose 'Options' on the Tools menu.

3.

Make sure that 'Download codes automatically' is checked on the first screen. When Windows Media Player encounters a video that's been encoded using a codec it doesn't know, it will attempt to download it automatically.
4. Click on 'OK' to complete the process.
Install the DivX Codec
5. Go to DivX.com (see Resources). The website will detect your operating system and automatically redirect you to the appropriate Web page.The DivX codec is a popular codec used to compress videos. Windows Media Player won't automatically download the DivX codec (if you try to play a DivX video, you will hear the sound, but not see any video). The following procedure will also work for other codecs that Windows Media doesn't automatically download.
6. Click on the 'Free Download' button on the right side of the page. The download should begin automatically. If it doesn't, click on the link to download the file.
7. Run the divxinstaller.exe file. Follow the prompts to accept the license agreement and install the software. When the installation is complete, you'll be able to play DivX-encoded movies in Windows Media Player.