If a customer complains that their monitor no longer displays a picture and you've confirmed it is powered on with the video cable securely fastened, what should you advise them to do?

Advising the customer to adjust the monitor's settings using the controls on the monitor is an appropriate first step because there may be an issue with the current display settings. Sometimes, the monitor may not be set to the correct input source (e.g., HDMI, VGA, DisplayPort) or the brightness and contrast settings may have been inadvertently changed, resulting in the screen appearing blank. By using the monitor's built-in controls, the customer can verify and change these settings, which may restore the display.

In the context of troubleshooting, adjusting the monitor's settings can often resolve simple issues without the need for additional hardware changes or software updates. This makes it a logical first step before considering more drastic measures like replacing the monitor or changing cables.