Why does my laptop screen have a line or a mark on it?

Screens produce a small number of distinct symptoms, and each one comes from a different place. The screenshot test settles the largest question in ten seconds, because a screenshot captures the picture before it ever reaches the panel. Getting that answer first stops people replacing a screen over a graphics driver, or spending an afternoon on drivers over a failed cable.

Step by step

1. Take a screenshot and view it elsewhere.Send it to a phone or another computer. If the fault is in the image, the panel never touched it and the cause is software. If the image is clean, the fault is in the display hardware.
2. If it is software, work through driver, application, setting.Update or roll back the graphics driver first, then check whether it happens in every application or only one, then look at resolution, scaling and colour profile settings.
3. If it is the panel, describe the fault precisely.A single dot that is always black is a dead pixel. A single dot always bright or coloured is a stuck pixel and sometimes recovers on its own. A full line the height or width of the screen is a connection or panel failure. A faint permanent ghost of something displayed for a long time is burn-in on an OLED panel.
4. Move the lid slowly and watch the fault.On a laptop, if a line appears, disappears or changes as the lid moves through its range, the video cable running through the hinge is the cause. That is a common, well-understood failure and a cheaper repair than a panel.
5. Check whether pressure changes it.Very gently, with a fingertip, at the edge of the bezel — not on the panel. If the fault changes, a connection is loose. Never press on the glass itself, and stop if anything flexes.
6. Connect an external monitor.If the external screen is clean while the laptop panel is faulty, the graphics hardware is fine and the fault is definitely the panel or its cable. If the external screen shows the same fault, it is the graphics hardware, which is a far more serious diagnosis.
7. Rule out flicker that is really a setting.Flicker that changes with brightness, or happens only on battery, is usually a power-saving or refresh-rate behaviour rather than a hardware fault. Try it plugged in, at full brightness, with adaptive brightness off.
8. Look up the manufacturer's dead pixel policy before claiming.One or two dead pixels are usually within the stated tolerance and will not be replaced under warranty. A line, a cluster or a spreading dark patch is a defect and is a different conversation.
9. Weigh the repair honestly.A hinge cable is cheap. A panel on an older laptop often costs a large fraction of what the machine is worth, and on some designs the panel is bonded to the lid assembly, which raises the cost again. Get a quote before deciding.

Tips

• Photograph the fault as soon as you notice it, with the date. Intermittent faults have a habit of behaving themselves the moment you reach a repair counter.
• A spreading dark blot with coloured edges is physical damage to the panel, usually from pressure or a knock. It will grow, and it cannot be repaired — only replaced.
• If the laptop is under warranty, do not disassemble anything. Opening it is what turns a covered defect into a rejected claim.

Common mistakes

• Pressing hard on the screen to 'fix' a line — Pressure damages liquid crystal panels permanently, and the mark it makes is not repairable. Gentle pressure at the bezel is a diagnostic; pressure on the panel is damage.
• Opening the lid assembly at home — The panel is fragile, the cables are fine ribbon connectors that tear, and a laptop display assembly carries a backlight circuit. This is a workshop job, and on a warrantied machine it voids the claim.

If it doesn't work

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