I am trying to take screenshots of window by following methods described at: http://guides.macrumors.com/Taking_Screenshots_in_Mac_OS_X If I use the SHORTCUT method then all the resulting images are just black. Nothing but just black screen. If I use Grab, then the resulting images are only white. What is the problem? I had taken screenshots using the SHORTCUT method and it used to work. Suddenly today its not working.