I think you are referring to the "Not Responding" caption which may appear in virtually any program's window when the CPU is overworked. If you open Windows Task Manager and click on "Applications" you will see programs that are "Running" if the CPU load gets very high this information will change for any that are 'held up' to "Not Responding". When the loading reduces the caption (both the program window and Windows Task Manager) will revert to normal. Where high demand software or several programs are running at once it is not uncommon for this to occur, especially on lower speed/older PCs often with less memory.
There are other problems which may also cause the above but they are less likely. For more info click here
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