This came to me as well when playing almost all the Call of Duty titles including Black Ops.When your system restarts or when the game freezes or so, this message appears.When this comes , all you have to do is press the 'No' button if you want the same fraphics settings that you have had put earlier. If ypu click on the 'yes' buttton, then it will go into 'Safemode' in which the graphics and resolution is fully reduced to its minimum capability.
Its up to you though. I always press the no buttton