Here's how I resolved a long-standing codec problem.
1. Uninstall Winamp. Winamp is known to cause some notorious codec issues.
2. If step 1 doesn't solve the problem, increase your RAM to 2.5 GB.
3. If step 2 doesn't solve the problem, uninstall EVERY media-related software, and ONLY install those that you need, such as VLC . You could also install K-Lite Codec Pack, which is really clean and stable.