I bought my desktop two years ago and I have a problem since then. When I try to open with a .mpg extension video with Quicktime 10.1, Here is the window I get: "additional softwares enabling QuickTime Player to open the video might be available". I went on the Apple Store. But it doesn't help at all. I tried to download softwares like the DivX one and MPEG streamclip. But it doesn't help either.