1) Have you installed any new hardware? If not I would google Windows Media Player and reinstall (but read on).
2) If you have recently changed your video card, then you need to clean the drivers, your temp folder, cache, and any driver installation foders before installing new drivers. To do it right you really need to defeat windows update, so that it does not automatically connect during system reboot and pork things again.
3) If you recently updated through Windows Update and any of your video cards showed up as devices with updates waiting. . . there's your problem. Return to step 2.