What Is Wrong With My Computer if There Are Lines Running Diagonally Through My Screen?

By Jane Williams

Lines on a monitor typically mean a problem with the cable, monitor or video card.
i Ryan McVay/Photodisc/Getty Images

Lines running across your business computer screen are a worrisome sign for most people. Monitors aren't cheap and if the lines are affecting a laptop screen, you might be looking into an even greater expense. But not all the news is bad. The cause for these lines can vary from a simple cable problem to the more complex video card failure. A second monitor helps diagnose the culprit to get you back to work.

Cable Problems

Before opening your computer tower and fiddling inside, check the monitor's video and power cables. A loose or failing cable can cause video problems, so grab each cable and give them a little wiggle as you watch the screen. If the lines change, a loose cord could be your problem. Tighten all connections between monitor and computer and monitor and wall and check for lines. If they persist, try swapping out the video cable for one you know is functioning properly. Use the suspected bad video cable on another computer and see if the lines appear. If they do, that cable is bad and needs replaced.

Video Card Issues

The monitor connects to the video card inside your computer tower to produce images on the screen, and if that card is faulty, the monitor will produce odd images. In some cases the video card comes loose, and this bad connection can cause the lines on your screen. Shut the computer down, remove the video card and reseat it firmly so its connections are tight and secure. Take this opportunity to clean the inside of the computer, as overheating can cause video problems as well. Once everything is reconnected properly, reboot and check for lines.

Out-Of-Date Drivers

A computer's hardware drivers are occasionally updated to ensure the device functions properly, and your video card's or monitor's drivers may be out of date. This can cause communication problems between the two pieces, which can result in lines and odd colors. Windows typically updates these drivers automatically if you have Windows Update turned on, but you can update them yourself by logging in as an administrator, clicking Start and selecting Control Panel. Under System and Maintenance, select Device Manager. You may be prompted for an administrative password. Once the Device Manager dialogue opens, select your video card or monitor by double-clicking it. Under the Driver tab, select Update Driver and Windows will walk you through the rest of the process.

Failing Monitor

If you've checked and double-checked your cables, reseated your video card and updated all drivers and the lines still mock you, the monitor itself may be going belly up. Connect a different monitor to your computer and check for lines. If they don't appear, try connecting the suspect monitor to another computer. Remember, a failing video card will show lines on any monitor, and a failing monitor will show lines no matter what computer it's connected to.