Dell Inspiron 8200 Problem

This is the second 8200 i had and have this problem with. The mouse just moves in some direction on its own and there is no way to stop it but i can control it to some measure by holding the little purple mouse in the middle of the keyboard in the opposite direction while using the mouse to navigate the screen. Has anyone else with this laptop encounter this problem? How can it be fixed?...if itcan be:upset: