What causes lines on your screen and how to tell what's wrong

Lines on your computer screen usually come from one of three sources: a loose cable, a graphics card problem, or a monitor defect. The type of line — whether it's horizontal, vertical, solid, or flickering — tells you where to look first. Before you replace anything, you can narrow down the cause in a few minutes by testing what you already have.

Start by checking whether the lines appear on your monitor's startup screen, before Windows or macOS loads. If they do, the problem is almost certainly the monitor itself or the cable connecting it to your computer. If the lines only show up after your operating system loads, the graphics card or its drivers are more likely at fault. This one test saves you from replacing the wrong part.

Key Takeaways

  • Lines that appear before your operating system loads point to a monitor or cable problem; lines that appear after point to your graphics card or drivers.
  • Reseating the cable — unplugging it fully and plugging it back in firmly — fixes loose connections and takes less than a minute.
  • Updating or reinstalling graphics drivers through Device Manager or your manufacturer's website often resolves software-related lines.
  • If lines persist after testing the cable and updating drivers, the monitor or graphics card itself may be faulty and need replacement.

Check and reseat your monitor cable

A loose connection is the most common cause of lines, and it's the easiest to fix. Shut down your computer completely — do not just put it to sleep. Locate the cable running from your monitor to the back of your computer tower or laptop dock. On a desktop, this is usually a DisplayPort, HDMI, or DVI cable. On a laptop, it may be a USB-C or Thunderbolt connection if you're using an external monitor.

Unplug the cable from both ends — the monitor side and the computer side. Look at the connector pins or contacts. If you see bent pins, corrosion, or debris, gently clean the contacts with a dry, lint-free cloth. Plug the cable back in firmly at both ends, making sure it clicks or seats fully. Turn your computer back on and check whether the lines are gone.

If you have a spare monitor cable of the same type, swap it in and test. A faulty cable can look fine but still cause lines. If a different cable eliminates the problem, replace the original one — they cost between $10 and $30 depending on the type.

Update your graphics drivers

If the lines appear only after your operating system loads, your graphics driver may be outdated or corrupted. Your graphics driver is the software that tells your computer how to communicate with your graphics card. On Windows, open Device Manager by right-clicking the Start button and selecting it from the menu. Expand "Display adapters" to see your graphics card listed.

Right-click your graphics card and select "Update driver." Choose "Search automatically for updated driver software." Windows will check for a newer version online and install it if one exists. Restart your computer when prompted. On macOS, go to System Settings, then Software Update, and install any available updates — macOS handles graphics drivers as part of the system update.

If automatic updates don't work, visit your graphics card manufacturer's website directly. NVIDIA, AMD, and Intel all offer driver downloads for their cards. read the latest driver for your specific card model and operating system, then run the installer. This often fixes lines caused by software conflicts or outdated code.

Uninstall and reinstall your graphics driver

Sometimes a corrupted driver installation causes lines even after an update. On Windows, open Device Manager again, right-click your graphics card, and select "Uninstall device." Check the box that says "Delete the driver software for this device" and confirm. Restart your computer — Windows will automatically reinstall a basic version of the driver.

Once your computer restarts, read the latest driver from your graphics card manufacturer's website and install it fresh. This removes any corrupted files and gives you a clean installation. Restart again when the installation finishes.

On macOS, driver reinstallation is not typically necessary because the system manages drivers automatically. If you're experiencing lines on a Mac, focus on the cable and monitor tests first, then contact Apple Support if the problem persists.

Test your monitor on a different computer

If you have access to another computer, connect your monitor to it using the same cable. If the lines appear on the second computer too, the monitor itself is faulty and needs replacement. If the lines disappear, the problem is with your original computer's graphics card or drivers — go back to the driver update and reinstall steps above.

If you don't have a second computer available, try connecting your monitor to a different port on your computer if one exists. Some computers have multiple video outputs — HDMI, DisplayPort, and USB-C, for example. Switching ports can help you determine whether the problem is with a specific port on your computer or with the monitor itself.

Adjust monitor settings and check for overheating

Some monitors have built-in settings that can cause line artifacts. On your monitor itself, look for a menu button — usually on the bottom or side. Navigate to settings or display options and look for anything labeled "refresh rate," "resolution," or "factory reset." Try resetting the monitor to factory defaults. This clears any settings that might be causing the lines.

Overheating can also cause display problems. Make sure your computer has adequate ventilation and that dust is not blocking air vents. If your computer is in an enclosed space or running very hot, move it to a cooler location and let it cool for 30 minutes, then test again. Check that your graphics card fan is spinning if you can see it — a stopped fan can cause lines as the card overheats.

When to replace your monitor or graphics card

If you've tested the cable, updated drivers, and confirmed the lines appear on a second computer, your monitor is likely faulty. Monitor replacement costs vary widely — a basic 24-inch monitor runs $100 to $200, while larger or higher-refresh models cost more. Most monitors come with a one-year warranty, so check your receipt or manufacturer's website to see if yours is still covered.

If the lines only appear on your original computer and persist after driver updates and cable replacement, your graphics card may be failing. Integrated graphics (built into your processor) cannot be replaced on most laptops, but on a desktop you can swap in a new card. Graphics cards range from $150 for entry-level models to $500 or more for high-performance ones. If your computer is several years old, this may be a good time to upgrade.

Frequently Asked Questions

Can I use my computer with lines on the screen while I fix it?

Yes, lines usually don't affect functionality — you can still use your computer while troubleshooting. However, if the lines are severe or flickering, extended use may cause eye strain. Prioritize testing the cable and updating drivers first, as these take only a few minutes and often solve the problem.

Why do the lines only appear sometimes?

Intermittent lines often point to a loose cable connection that makes and breaks contact as the cable moves slightly. They can also result from a graphics card that overheats during heavy use and cools down during idle time. Test the cable first, then monitor your computer's temperature using free tools like HWiNFO or Macs Fan Control.

Do I need to buy a new monitor if the lines won't go away?

Not necessarily. If you've ruled out cable and driver problems, the monitor may still be under warranty. Contact the manufacturer with your proof of purchase — many will repair or replace it for free within the first year. If it's out of warranty and the lines are minor, you may choose to keep using it rather than replace it.

What's the difference between horizontal and vertical lines?

Both usually come from the same causes — loose cables or graphics problems — but the direction can sometimes hint at which component is failing. Vertical lines are slightly more common with graphics card issues, while horizontal lines can indicate monitor panel failure. However, test the cable and drivers regardless of line direction, as these steps fix most cases.

Will a factory reset of my computer fix the lines?

A factory reset will not fix lines caused by hardware problems like loose cables or a failing monitor. It may help if a corrupted driver is the cause, but updating or reinstalling the driver is faster and less disruptive. Only resort to a factory reset after you've tested the cable, updated drivers, and ruled out hardware failure.