|That depends on whether the blue line on your screen was put there with a marker pen.|
Q1. Is this a laptop or desktop system?
Q2 Is it a CRT monitor or LCD?
Q3 What does any of this have to do with NETWORKING?
Post a detailed description of your problem including full system credentials. Include advice on whether this blue line appears during bootup or only when the operating system is running. If the monitor is a separate unit, Disconnect it from the PC, turn it on and see if the line is still there.
Finally, Post your question in an appropriate forum such as General Hardware or Vista
Goin' Fishin' (Some day)