There is a Unknown Line going across (not straight though) my screen and the color display on the line is slightly different than other area of the monitor, hence it is very much visible . Its getting bigger day by day and today I just noticed that there another small line is coming from the top of the monitor. What could be the reason for this , is it due to weather changes or due to any power fluctuation or is it because I keep it on for 18 hours a day. The LCD Monitor is almost 5 years old but my 7 year old CRT Monitor still works awesome.
It is simply failing.
It can be due to anything - weather is unlikely, but if you go through extreme changes, it is possible that a component can stretch then shrink and simply fail.
18 hours a day usage can also be a factor.
The truth is, it can be a number of things, I see quite a few monitors fail and it is hard to pick a single reason for it.
You can try putting (a small amount of) pressure on the frame at the end of the line as that sometimes helps - it works on a few laptops, but, this is just a small work around and it will get worse over time.
Could well be a row of pixels that are misbehaving - this usually means that one or more of the edge contacts on the back of the LCD panel are coming loose. You might be able to verify this by gently pushing round the edges of the display to see whether the problem gets better or worse. Unfortunately, if it is the display contacts they can be a pain to fix as they are often just metal foil strips stuck onto glass-mount contacts using a sticky plastic film and attempts to stick them down again can be hit-and-miss - you can end up making the problem worse just by disturbing the panel as you remove the bezel.