Final answer:
When the monitor shows a straight line, troubleshooting should start by checking cable connections, adjusting display settings, and testing the monitor on another computer.
Step-by-step explanation:
When the monitor shows a straight line, the first step in troubleshooting is to check the cable connections. Ensure that the monitor's power cable and video cable are securely plugged into the computer and that there are no loose connections. A loose or faulty cable can result in a straight line or no display on the monitor.
Another possibility is that the monitor's display settings may need adjustment. Check the settings on the computer to ensure that the correct resolution and refresh rate are selected for the monitor.
Lastly, if the above steps do not resolve the issue, it could indicate a problem with the monitor itself. Try connecting the monitor to another computer or use a different monitor to determine if the issue lies with the monitor or the computer.