Run the dead pixel test Solid full-screen colors make a line easy to see, so you can note exactly where it sits and what color it is before you start swapping cables.
On this page
How we checked this: we haven’t reproduced these faults on our own hardware. The steps come from monitor and laptop makers’ support pages (Dell, LG, ViewSonic, AOC), linked in the sources and checked on 2026-10-25. Menus differ between models, so if yours doesn’t match, tell us. More on our method on the How We Test page.
A thin line down the middle of the screen. Or a band of flickering horizontal stripes across the top. Either way, it’s hard to stop looking at.
Lines can come from three places: the cable and port, the computer (graphics card or driver), or the monitor itself. One simple check splits those apart, and it costs nothing.
Panel or signal? The one-minute menu test
Press the monitor’s menu button so its own on-screen menu appears. That menu is drawn by the monitor, not your PC. ViewSonic’s support article puts it plainly: lines over the menu point to a hardware or panel failure, and lines that aren’t on the menu mean the monitor is fine and the cable, graphics card or PC is the issue.
Want a stronger check? Unplug the video cable. LG’s vertical lines page says that if lines still show on the “No Signal” screen in the same place, the monitor needs a technician. Dell monitors have a built-in self-test for the same job, and Dell’s diagnostics guide says any lines visible during it mean a problem with the monitor.
| What you see | Likely cause | Where to go |
|---|---|---|
| Lines over the monitor’s own menu, or on its No Signal screen | Panel or monitor electronics | When it’s the panel |
| Lines on the desktop, clean menu | Cable, port, graphics card or driver | Fix 1: cable and port |
| Lines only at one refresh rate or resolution | Signal timing or bandwidth | Fix 2: settings |
| Lines started right after a driver or Windows update | Graphics driver | Fix 3: driver |
| Lines on a laptop’s own screen, external monitor fine | Laptop panel or its internal cable | Laptop section |
| A thin line, one pixel wide, that never moves or changes | A row or column of pixels failing | When it’s the panel |
One more trick: take a screenshot and look at it on another device. If the lines are in the screenshot, they’re part of the image the computer is making, so the monitor and cable are off the hook.
Fix 1: Cable and port
The cable is always “definitely plugged in”. Check anyway. It takes ten seconds, and it’s the first thing every maker lists.
- Unplug the video cable at both ends and look at the plugs. LG says to check for damaged pins or debris, and to replace a damaged cable. Plug it back in firmly. Expected result: lines gone, or no change.
- Use the cable that came with the monitor. LG warns that a cable that doesn’t meet the monitor’s specs can cause noise and other display problems.
- Take out the middlemen. AOC’s support FAQ says to connect directly, without adapters, extension cables or docking stations.
- Try the other connection type, HDMI instead of DisplayPort or the reverse, and a different port on both ends. AOC suggests the same.
- On a desktop with a graphics card, plug into the card’s ports, not the ones on the motherboard. Dell’s monitor troubleshooting article calls the wrong port a common cause of display trouble on gaming PCs.
- Unplug the monitor’s power for a few minutes, then reconnect it (another AOC step).
If the lines follow the cable to a second monitor, bin the cable. If they stay on this monitor with a different cable and a different computer, skip ahead to the panel section.
Fix 2: Resolution, refresh rate and the monitor’s reset
- Set the resolution Windows marks “Recommended” under Settings > System > Display. That’s the monitor’s native one.
- Pick a refresh rate from the monitor’s spec sheet under Advanced display. If you’ve overclocked the monitor or enabled an “OC” mode, turn it off for now. Dell lists an overclocked refresh rate as a cause of flicker, so rule it out here too.
- Reset the monitor to factory settings from its menu. ViewSonic calls it Memory Recall or All Reset. Dell’s S2716DG troubleshooting table puts a factory reset first for horizontal and vertical lines.
- Using VGA? Run the monitor’s Auto Adjust. The same Dell table lists Auto Adjust and the Phase and Pixel Clock controls, which apply to analog input.
Lines that appear at only one refresh rate are worth noting before you contact support. In an August 2025 r/Monitors thread, a Gigabyte M27QX owner saw horizontal lines only when the monitor dropped to 120Hz for a PS5. Replies split between a panel defect and the HDMI connection, and a ViewSonic owner with the same symptom said they’d filed an RMA. So: try a different cable and input first, then treat it as a warranty question.
Run the refresh rate test after any change to confirm the rate you picked actually stuck.
Fix 3: Graphics driver and the computer
If the menu test came back clean, the driver is the next suspect, especially if the lines showed up after an update.
- Restart the graphics driver: hold Windows + Ctrl + Shift and press B. Dell’s guide lists this first for lines. The screen flashes once. That’s normal.
- Roll it back if the lines started after an update: Device Manager > Display adapters, right-click your graphics adapter, Properties > Driver > Roll Back Driver. If the button is grayed out, install the latest driver from NVIDIA, AMD or Intel instead.
- Dell also suggests Windows’ Video Playback troubleshooter: Start > Settings > System > Troubleshoot > Other troubleshooters, then Run next to Video Playback.
- Connect the monitor to another computer, a laptop or a console. ViewSonic suggests this to rule out the graphics card.
Clean on the other device but lines on yours, with a fresh driver and a known good cable? That points at the graphics card. Lines that also show up in screenshots point the same way.
Lines on a laptop screen
You can’t swap a laptop’s internal cable, so the checks change a little.
- Plug in an external monitor or TV. If it’s clean while the built-in screen has lines, the laptop’s panel or its internal display cable is the likely cause. Lines on both screens point back to the graphics driver or hardware.
- Run the maker’s screen test if there is one. Dell’s LCD built-in self-test starts with the laptop off: hold D and press the power button, and the screen cycles through solid colors. Dell says lines during that test mean the screen itself is likely faulty.
- No maker test? Restart and open the BIOS or UEFI setup screen (often F2, F10, Del or Esc, depending on the brand). That screen doesn’t use Windows’ graphics driver, so lines there point to hardware.
- Note whether the lines change when you move the lid. That detail helps a repair tech decide between the panel and the cable that runs through the hinge.
More laptop screen fixes are on the laptop hub.
When it’s the panel: what to do
Lines over the monitor’s own menu, on its No Signal screen, or in a built-in self-test mean a hardware fault. Software won’t fix it, and neither will a stuck pixel fixer. A whole row or column that’s out usually comes from a connection fault inside the panel, as Wikipedia’s defective pixel article explains.
- Don’t press, tap or flex the panel. LG notes that impacts or pressure on the screen can cause vertical lines in the first place, and pressing can make a fault worse. We don’t recommend it on any screen.
- Don’t open the monitor. There’s nothing user-fixable inside, and opening it can affect the warranty.
- Check ventilation. LG lists overheating as a possible cause, so make sure the vents aren’t blocked, then see if the lines change once it has cooled.
- Gather evidence: run the dead pixel test full screen, photograph the lines on a solid color, and note the model and serial number. ViewSonic asks for the serial number for service.
- Contact the retailer or the maker (see below).
If it can’t be fixed
On a new monitor, the return window beats any fix. Retailer returns and the maker’s warranty are separate, so check the store’s return period first, then the maker’s warranty terms for your model and region. Lines that show in the monitor’s own menu or self-test are a hardware fault every maker in our sources sends to service. Keep the photos and the serial number handy, and mention whether the lines change with refresh rate, input or temperature. If the monitor is out of warranty, get a repair quote and compare it with the price of a new monitor before you decide.
Frequently asked questions
Why are there lines on my monitor screen?
Usually a loose or faulty cable, the wrong port, a graphics driver problem, or a fault in the panel itself. Open the monitor’s own menu: lines over the menu mean the monitor, a clean menu means the cable, port or computer.
Can a bad HDMI or DisplayPort cable cause lines on the screen?
Yes. LG and AOC both list a damaged or unsuitable video cable as a cause of lines. Reseat both ends, then swap in the cable that came with the monitor and connect without adapters.
How do I know if the lines come from my graphics card or the monitor?
Connect the monitor to another computer, and connect another screen to your computer. Lines that follow the monitor are the monitor. Lines that follow the computer, or show up in screenshots, point to the graphics card or driver.
Can vertical lines on a monitor be fixed?
If they come from the cable, settings or driver, yes, often in minutes. If they show on the monitor’s own menu or self-test, it’s a hardware fault that needs a repair or replacement under warranty.
Will a stuck pixel fixer remove a line on my screen?
No. A full line of pixels that’s out usually means a connection fault inside the panel. Pixel fixers can only sometimes help single stuck pixels.
Related fixes
- Dead pixel test (free tool)
- Monitor flickering? How to find the cause and fix it
- Stuck pixel on your monitor? How to tell and fix it
- 144Hz monitor showing 60Hz? How to fix it
- Monitor fix guides
- Laptop screen fix guides
Sources
- ViewSonic: What should I do if vertical or horizontal lines appear on my monitor?, checked 2026-10-25.
- LG Canada: Vertical lines on screen [monitor], checked 2026-10-25.
- Dell: Fix Dell monitor display issues, checked 2026-10-25.
- Dell: How to run the Dell monitor built-in diagnostics, checked 2026-10-25.
- Dell: How to run the LCD built-in self-test on a Dell laptop, checked 2026-10-25.
- Dell: How to use and troubleshoot the Dell S2716DG monitor, checked 2026-10-25.
- AOC: Support FAQ (lines and disturbances), checked 2026-10-25.
- Wikipedia: Defective pixel, checked 2026-10-25.
- r/Monitors: Horizontal lines on monitor if I switch to a lower refresh rate (Aug 2025), checked 2026-10-25.
