A vertical line running down your computer monitor's screen usually is related to pixelation of the screen. Colors on the screen wear down over time and can actually dye and discolor the screens. The problem also can show up on flat-panel monitors that have been bumped. Such jolts can cause distortion of the display--sometimes in the form of a strange line down the center of the monitor.
Power down your monitor. Leave the monitor powered down for several minutes. Sometimes your monitor just needs a few minutes to cool down.
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Power the monitor back on and see if the line is still there or not.
Look at the cable connection running between your monitor and your computer. Make sure the cable is inserted completely into both devices.
Launch your Internet browser and make your way to the website of your monitor's manufacturer. Search in "Support" for your model of monitor, then download any available drivers for the device. The drivers can often correct the problem. Look for the driver marked "monitor."
Power down the computer, remove the cables and open the computer case. Find the video card connected to your motherboard. The video card is where the monitor connects to the PC. Remove the card from the PCI (peripheral component interconnect) slot and move it to a different slot.
The PCI slot allows you to connect additional hardware to the computer's motherboard, but there might be a problem with the PCI slot. Once the video card is reinstalled, close the computer case and connect the cables to the computer. Power it on and the line should be gone.