One white dot (1 pixel in size), may appear on the top-left corner of the screen in the following scenarios:
In Windows 7 Home Basic Edition, the issue may occur after a user selects the "Windows 7 Basic” color theme and changes the wallpaper.
In Windows 7 Ultimate and other editions listed in the "Applies to" section, this issue may occur after a user selects an Aero theme and then un-checks “Enable transparency”.
This is a known issue in Microsoft Windows 7 with certain themes.
Microsoft has confirmed that this is a by design issue in the Microsoft products that are listed in the "Applies to" section.