Check and reseat the video cable at both ends
Try a different HDMI, DisplayPort, DVI, or VGA cable
Use a different port on the monitor and computer
Test the monitor with another device
Test the computer with another monitor
Lower the refresh rate in display settings
Set the native resolution of the monitor
Update or reinstall the graphics driver
Restart the computer and monitor
Check for bent or damaged cable pins
Disable overclocking on the GPU or monitor
Run the monitor self-test or built-in diagnostics
Check for magnetic interference near the monitor
Clean the monitor screen gently
Reset the monitor to factory settings
Replace the monitor if the lines remain on all devices