You've installed a codec pack you shouldn't and it's ruined your system codecs - uninstall it. Chances are though, being the dodgy codec pack it is, it'll remove legit codecs too when you do that, so that'll not fix anything, only remove the problem software. From there, you install good copies of codecs, not using codec packs. In summary, codec packs are evil Also avoid RealOne/Real Player/variants.

Or the simple solution, reinstall Windows (and this is not a joke like in other threads), since that will fix broken codecs too You'll still have to install good copies of newer codecs afterwards though to play newer things like DivX/XviD.