Check the monitor cable connections
Reseat the HDMI, DisplayPort, DVI, or VGA cable
Try a different cable
Try a different port on the monitor
Try a different port on the computer
Restart the computer and monitor
Test the monitor with another device
Test the computer with another monitor
Lower or change the screen resolution
Change the refresh rate
Update the graphics driver
Reinstall the graphics driver
Check for loose or damaged monitor cables
Reset the monitor to factory settings
Disable any overclocking settings
Check the monitor for physical damage
Move the monitor away from electrical interference
Make sure the graphics card is properly seated
Check the GPU temperature
Replace the monitor if the lines remain
Replace the graphics card if the issue follows the computer