1. Turn on your computer and wait for your edition of Windows 7 to load into your desktop. Open a Web browser.
2. Download a codec pack like CCCP, K-lite or Media Player Codec Pack (check the Resources section of this article).

3. Double click the codec pack that you just downloaded and it will install onto your computer. These codec packs come with every single codec you could need to play any type of video file there is.
4. Restart your computer after the codec pack installs. Open your video file by double clicking it. It will now play with no errors.