Download the Latest Version of Windows Media Player
1. Launch your web browser by double-clicking its icon on your desktop. Go to the Windows Media Player page of Microsoft's website (see Resources). Locate your operating system in the left-hand column and then click on the link in the right-hand column ('Recommended Player version').
2. Download Windows Media Player. Click the 'Download Now' button if you are downloading WMP version 10 or earlier. Click 'Continue' if you are running Windows Vista and downloading WMP 11. Then enter your 25-digit Microsoft Product Key (located on the green sticker on the base of your laptop or on your desktop tower). Click 'Download Now' after validation.

3. Install Windows Media Player by clicking 'Run' or 'Install.' Click 'OK' to begin the installation wizard, then click 'Next' or 'OK' to progress through each stage of the installation. Click 'Finish' to complete the installation.
4. Restart your computer.
5. Open Windows Media Player and try to play the video or audio file that prompted the error. If you still receive a 'fix codec error,' proceed to Section 2.
Turn On the Auto-update Function
6. Launch Windows Media Player by double-clicking its icon on your desktop.
7. Click on 'Tools' in the top menu bar and then highlight and click 'Options.' If you do not see 'Tools' or a top menu bar, click on the 'Layout Options' button (it looks like a square) and then highlight and click 'Show Classic Menus.'
8. Click the 'Player' tap in the 'Options' application window. Check the box next to 'Download codecs automatically' and then check the box next to 'Once a day' to set the frequency of downloading codecs.
9. Try to play the video or audio file that prompted the error. Wait 24 hours for WMP to download all the codecs available then try and play the file again.