Codecs?

Ok, I installed a pack of codecs to play some movie with a mp4 format. Turned out that not only that I never succeeded in playing that movie - since then I can't play ANY movie. The computer freezes, and when I try for example to alt+tab back to the desktop, it moves with about 3 screens per second. I can't even run some of the games I have on, because the exact same thing happens.

What the hell is going on? I would be really grateful if someone helps me...





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