I can't seem to play some of my videos on windows media player~it says there is an error finding the codec. What can I do to get them back???

When I bought this new laptop media player worked fine, Soon I had to reboot from the installation discs and it hasn't worked since.
I get the same message or "can't find disc". Nothing on their site can fix it.
I went with I Tunes by Apple and gave up on windows media player.

http://www.divx-digest.com/software/nimo_pack.html

Thanks Shifty, that did it.