Why do YouTube videos looks so fuzzy and bad quality?

Now before you say that i need to wait till theyre fully processed or some other theory, i want to say that before the videos were at a normal or decent quality, but now it is horrible. Ive just changed my video card from a 9800gt to a 9800gtx, which is supposed to make my computer have better quality, but ever since the change youtube has looked so pixelated and horrible. please help.Why do YouTube videos looks so fuzzy and bad quality?could be your browser