You did not say much about this line.
Color, placement, if it is there after you logon, what type of monitor
(brand/make/model/age), how the monitor connects, what type of video card,
how up to date the video drivers are, etc.
Are you talking about a trinitron based monitor. They all have two very thin
horizontal wires which show up if you look very closely. A bit more info
would help people narrow down your problem.