A line on your computer screen can come from the display panel, its connection, or the image the computer is producing. The quickest useful checks are whether the line appears in a screenshot viewed elsewhere, whether another display shows it, and whether it remains during the manufacturer’s built-in screen test.
A thin vertical stripe does not automatically mean you need a new monitor, and a horizontal line does not automatically identify a graphics-card fault. Work through the checks below in order. Stop early if the screen is cracked, there has been a spill, or you notice an electrical smell or unusual heat.
What does the line look like?
Write down whether it is vertical or horizontal, fixed or moving, and present everywhere or only inside one application. Note when it first appeared: after moving the desk, connecting a dock, installing an update, or an impact. A phone photograph can preserve the symptom for support, although photographs can also introduce bands that you cannot see with your eyes.
Move an ordinary window across the affected area. A line that stays at the same physical position while the window moves suggests a different problem from a border that moves with the window. Neither observation proves which component failed. Save your work and restart normally once before making more changes.
Does the line appear in a screenshot?
Take an actual screenshot using the operating system, then open that file on another known-good device. Viewing it only on the suspect screen defeats the purpose: a physical panel line would still cover the picture. Compare the saved image with what you can see directly on the display.
If the line is embedded in the file, investigate the application, image content, or graphics-rendering path. If it is absent, the panel, cable, connection, or a later stage of display output becomes more suspicious. This is a screening clue, not a definitive panel test. Intermittent faults, video overlays and capture timing can make screenshots misleading; a clean capture cannot certify that the graphics hardware is healthy.
Check the external cable before buying anything
For a separate monitor, shut down the computer and turn off the screen before rearranging connections. Reseat both ends of the video cable, holding the connector rather than pulling the lead. Release any latch first. Look for damaged plugs, sharp bends or tension, but do not poke tools into ports or attempt to straighten damaged contacts.
Try a known-working cable that supports the same connection and display mode. Where compatible, bypass the dock, adapter or KVM switch and connect directly. Change one thing at a time so you can identify what helped. ASUS’s monitor troubleshooting guidance recommends checking cable seating, substituting a suitable cable and comparing another screen or computer.
If the problem disappears only at a lower supported refresh rate, record that result. It points toward a mode-dependent problem worth investigating, rather than proving that the panel or cable alone is defective. Our DisplayPort cable guide covers matching the connection’s capabilities.
Compare another display or another computer
Connect a laptop to a known-good external monitor using a supported port and cable. Select an appropriate display mode so the external screen actually shows an image. Compare the same ordinary content on both displays. For a desktop, substitute another monitor if available; Dell includes this comparison in its display troubleshooting.
A clean external picture makes the laptop’s internal display path more suspicious, but does not isolate the panel from its internal cable or electronics. Problems on both screens justify investigating shared software or graphics hardware. If the suspect monitor shows the same line with another computer and suitable cable, the monitor itself becomes the stronger suspect.
Use a built-in diagnostic, not a random repair video
A monitor’s own diagnostic can show test patterns independently of the computer. For Dell monitors, find the exact model’s manual and follow its built-in diagnostic procedure. Button sequences vary. Dell distinguishes this from the basic self-test used for blank-screen checks; its monitor diagnostic guide directs users with lines to built-in diagnostics.
If the line remains in those internally generated patterns, contact the manufacturer about repair. If it does not, continue investigating the incoming signal and computer. Record which colors show the defect rather than treating a brief clean screen as a complete pass.
For supported Dell laptops, the LCD self-test instructions call for shutting down, disconnecting peripherals, connecting the charger, then holding D while powering on until test colors appear. Follow the current model guidance. This checks screen hardware, not Windows or its drivers.
On ASUS devices, the manufacturer also recommends checking the BIOS display. Enter it only through your model’s documented method and leave settings unchanged. A line visible before Windows loads supports a hardware investigation. A clean BIOS screen does not rule out intermittent or workload-dependent faults.
Investigate software when the pattern fits
If the line appears only in one app, update that app and compare other programs before replacing hardware. If the trouble began immediately after a graphics-driver update, use the computer manufacturer’s supported troubleshooting process. Avoid unofficial driver-download utilities; ask IT first on a managed work computer.
For flickering or scrambling alongside the lines, Microsoft recommends comparing Task Manager: flickering there too suggests the driver, while a stable Task Manager suggests an incompatible app. This test concerns flicker and is not a diagnosis for a permanent stripe. Microsoft also documents driver updating or rollback when appropriate.
When should you arrange repair?
Seek service when a line persists in hardware diagnostics, follows the monitor across computers, or accompanies visible damage. Give support the model, photographs and results of your comparisons. Do not squeeze the bezel, press on the panel, apply heat, or open the casing. Keep important files backed up while the computer remains usable.
If testing points to the external cable, browse monitor cables on Amazon and match both connectors and the supported display mode. Borrowing a suitable cable first can prevent an unnecessary purchase.
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