Diagnosis
A persistent vertical artifact is often caused by signal interference, a failing panel driver, or physical pressure damage.
How to Fix It
First, isolate the source. Power off the monitor. Disconnect all video cables. Power it back on to the 'No Signal' screen. If the line is still present, the issue is internal to the monitor's panel or electronics. Perform a monitor self-test: with no cables attached, the 'No Signal' message should appear. Observe the line during this test.
If That Didn't Work
If the line only appears with a signal, the problem is likely in the signal path. Use a different PC or gaming console with a known-good cable. If the line disappears, the fault is with your original source device or its graphics output. Update your graphics drivers.
Heads Up
Physical pressure on the screen, especially during cleaning or transport, can cause permanent vertical lines. This is a panel defect, not a setting. If the line is visible on the 'No Signal' screen, you will need to contact ViewSonic support for a warranty assessment.