Hmmm... I've had similar problems before, but I can't really remember the precise steps that I used to get up and running again. If you haven't already re-installed a whole bunch of stuff, then I'd say do a format and reinstall Windows & SP2, but have a backup copy of all the codecs you've downloaded, plus a good third-party player.
Media Player Classic is good, though I've had some issues when skipping around in bigger movies, but it should at least be enough to let you know if things are working again.
Once you do the reinstall, make sure to install the most recent/most stable version of your video drivers, then install all the codecs and run it through MPC. If it works, then great, if not, um, well I'm doing the same thing on Thursday or Friday so I'll let you know how it goes.
Re: OT: Video-codec problem, avi, mpg, etc, system
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