A number of issues cause vertical lines on your computer screen, ranging from software incompatibilities with the computer's drivers to hardware problems involving the magnetic field of the monitor. There are two general solutions for fixing the problem--degaussing the monitor and updating your video card drivers to the latest revision.
Degaussin
Open the monitor's menu by pressing the on-console button for the menu features. This will be one of the buttons on the face of the monitor. If you are having trouble locating the button to press, consult the operating manual for your particular model monitor.
Cycle through the menu options with the "+" and "-" buttons on the monitor until you find the "Degauss" option.
Select the "Enter" key to degauss the screen. This will realign the magnetic field of the monitor, potentially solving your issue.
Update drivers
Go to the website for your video card manufacturer and visit the "Support" page. The product documentation for your computer should include the manufacturer and model number for your video card. If you no longer have your computer manual, visit the manufacturer's website; there should be a PDF version available in their "Support" section.
Click on the "Downloads" section of the support page and enter in your specific video card model number to locate your required driver.
Download the driver and save it to your desktop.
Double-click on the installation file to commence the procedure. Follow the on-screen instructions to update your driver, which usually consists of agreeing to a licensing agreement.
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