I work for a non-profit that recieved a donated computer. The screen that contains the user name and password box has an inappropriate picture as a background. I tried going to the control panel/display controls, but the options there will only let you change the screensaver or background for the desktop. I tried creating a new user and this gave me a fresh desktop, but the loggin screen with the inappropriate picture remains the same. How do I get rid of this thing?