Has only just started doing this, as soon as I want to watch a movie from my lappy and plug it into the TV (hdmi) the screen changes and turns on its side (also effects the mouse)
Saw this on a different website:Its a minor desktop rotation issue. Look into your display driver settings (ATI Catalyst Control Center, Intel Display Settings, nVidia Forceware etc), there has to be an option to change the display rotation.