yes QT is a diva on win7. It's much more complicated than reinstall it. At first I would try to set video to save (gdi mode) in the QT system preferences (extended tab). A wrong setting at this even let the browser crash during QT playback. Second I would check that the needed file extension for your program e.g. .mov is linked to QT. That's what VLC has done to the described win "k" system, not directly but it checks for proper media file linking during installation and repair it if needed. WMP and some other players grap the QT file formats e.g. .mov but can't play some of it because it's only a container and they haven't the appropriate codec to play the content.