If you're seeing pc screen lines unexpectedly, the issue could be related to a loose display cable, outdated graphics drivers, or a failing monitor panel. Make sure all cables are connected and to make sure your graphics drivers are up to date. You may also hook a PC up to a second monitor to see if the issue is due to the screen or the computer. The visual artifacts may be caused by overheating the graphics hardware or by setting the display incorrectly. By taking a step-by-step approach to troubleshooting, one can help determine the exact problem.