It sounds like you may need to adjust the video mode. To check this, go to Windows Program Manager. First, open the Main icon group, and then the Control Panel/Driver's Applet. Double click on the [MCI] Microsoft Video for Windows or [MCI] Microsoft AVI Video driver so that it will open. A pop-up screen will appear. Make sure that the Video Mode is set to Window, NOT FULL SCREEN. The Zoom by 2 option SHOULD NOT be selected either. But, Skip Video Frames if Behind should be selected. Now, close the Window. Your videos should play correctly in the future. While some video cards are able to handle a full screen video mode setting, others cannot.
