When you find computer screen lines vertical, start by doing simple troubleshooting. Restart the system and check if the lines disappear. Secondly, replace or reinstall the graphics card drivers since corruption of drivers may lead to display artifact. It is also a good idea to have the monitor connected to a different device in order to eliminate hardware issues. When the lines continue to appear on several devices, then the monitor panel may be malfunctioning and this may need to be repaired or replaced depending on the seriousness.