hi it sounds like the graphics card if you change the size it may help it or if its a nvidia graphics card like most are then if you go into the nvidia settings (right click on desktop then onto the nvidia name) then you can set it up to do 2 screen sizes your laptop and extra screen or tv
most of the time the laptop screen will go smaller then connected to a screen or tv as it changes the settings so it will work the best it can the bigger the screen sometimes not all but some it will make the screen go smaller
