Quicktime Yes Mediaplayer No

So Heres the Deal.

No videos with play on Mediaplayer, Realplayer, Divx Player, anything. All I get is audio.

However, Quicktime does work. I can play anything on that. Works Fine.

Now, this problem just arose out of no where...I have had this computer for years and cant seem to beat this problem.

Any helpful tips?

-Daniel-