I had this similar problem with a clients computer. My tech guy solved it in an instant remotely. Open your windows media player, r click over the top tool bar to bring up the tools tab, click options, performance, use the slider and move it to none. The hardware processing kicked in and causes this weird effect. So by sliding it to none, the processor doesn't effect it. It worked for my client. Hope it works for you.
Czorn
June 2009