Why did my Windows Media player lose the capability to play mp4s?

Close the file, click right, open with, then with iTunes.
If it does not work, you have to download iTunes setup, go to :
http://www.download3k.com/Install-iTunes.html
download for free..
then do first option again.
For some reason my Windows Media Player can no longer play mp4 files. I had converted some videos from mpg to mp4 format so I could upload them on my Zune, then when I would watch them I would choose to play them on Windows Media Player because it has a much better screen and I am more comfortable watching videos with it. All of a sudden I lost that capability. I want to know why but most of all I want to know how to fix this situation.
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sounds as though the video codec has become currupt, normally happens when something overwrites it, but if you search for CODEC LITE pack in yahoo or google, download and install, this will give media player the ability to play MP4 vids
I don't know.
In case you can't fix the problem, try VLC. It's free, it doesn't need any external codecs, and it plays pretty much everything, including mp4. If your mp4s don't work with vlc they most likely are broken.
http://www.videolan.org/vlc/
if u have itunes it probably has taken control of mp4's. uninstalling itunes may fix the problem