I would first check the connection of the monitor on the rear panel of the chassis and if you are having video card installed in your system open the chassis and properly fix it in the slot it happen mostly due to loose connection and if not the monitor must be defected one or attach the monitor to some other machine and check if its working it might me relating to the display drivers. Check in the Device manager and in the display if you find any yellow colored question mark it means the driver are gone bad an you need to install new driver for your Video card and still if the vertical are seen you need to try another add on Video card and find out whether the monitor does not display the vertical line and if still the vertical pattern line are displayed it’s a problem relating to the monitor and you need to repair it from the authorized person.