Download and install the K lite codec pack  from here   it should give you almost any codec that you need.
I was hoping you could help me. I reinstalled windows and windows media player 11. Everything is working fine, except my tv tuner does not work. When I try to watch or record TV, I get an error message saying the decoder is missing. I have tied downloading drivers from Dell, ATI, and my Dell drivers disk but I still don't had a solution. I think I am missing a MPEG-2 codex. Can you tell me where I can find this please?
I reinstalled Windows and I have a video codex error.