The projector resolution is different then the laptops screen. Just go into the properties and change it to whatever it looked like before. (1440x800, 1680x1050, etc.) It's probably running at either 640x480, or 800x600.
I try to change the resolution once the projector working but the resolution can't change same as previous (1680x1050) prior connected. Do you have any idea? Thank you very much.