Graphics card shows lines or artifacts

The cable, monitor, driver or graphics memory may cause visual corruption.

Stop if there is smoke, a burning smell or severe graphics corruption under load. Avoid speculative stress tests, overclocking or power-supply work.

Save your work and stop games or other heavy graphics tasks. Stop testing if there is a burning smell or unusual noise.
Check whether the monitor menu or startup screen is affected too. Photograph the fault without personal information.
After switching off, test another suitable cable or monitor. Never force connectors.
If it occurs only in Windows, check the appropriate official graphics driver. If it persists before Windows with another cable and monitor, seek qualified help instead of stress-testing or overclocking.

Test after each step and stop when the issue is solved. Checkmarks are not permanently saved.