To check the brightness and contrast settings.
1. First find the brightness and contrast settings on your monitor.
2. Then examine the above image. You will see an 11-step graduated grayscale bar. Adjust your monitor controls until 0% is pure white and 100% is pure black, and every step in between is visibly different from the one on either side.
An inability to get the controls far enough to one direction or another to do this typically indicates a monitor that is aging and unable to display the full, normal range of brightness and contrast.