Bad Video Projection

I am using a Dell Latitude D820 running Windows XP Pro SP2 and PowerPoint 2003 SP2.  I am projecting the PowerPoint presentation with imbedded Microsoft Media Player video clips via VGA to a Mitsubishi projector.  If I run the laptop on the internal battery, it works fine.  If I plug the laptop into the 110 volt adapter, the video clip in Windows Media Player projects as a wide very narrow image.  Can anyone tell me why and what to do about it.  Is it a setting having to do with the video refresh rate on the projector, in Windows or the Video Player?