KB Article: http://support.microsoft.com/kb/939206

INTRODUCTION

Consider the following scenario:

  • You are using a Windows Vista-based computer.
  • You have Aero Glass disabled, or the video card does not support this mode.
  • You are playing a video in Microsoft Windows Media Player.
  • You are playing the video in full-screen mode.
  • You right-click the full-screen video to display a shortcut menu.

In this scenario, the video playback window becomes unresponsive. If you press CTL+ALT+DEL to exit full-screen mode, Windows Media Player functionality returns.