|Manufacturers commonly specify that LCD displays can have up to a tiny number of random bad pixels - always black or white or the wrong color, but errant lines of a color are not normal (ones longer than say 1/16") . |
Lines are almost always caused by a hardware problem, usually of the monitor itself, not a software problem.
By the way, never unplug or plug in the monitor's data cable while the computer is running. They're NOT "hot pluggable".
If you're plugging it into a video card (that installs in a mboard slot; it's not built into the motherboard), you could try unplugging the computer's PS, re-seating the video card (remove it's hold down screw, remove it, install it, make sure it's all the way down in it's slot, install it's hold down screw), then restoring the AC power and trying the computer and monitor, but it probably won't help.
Try the monitor with a different computer. If you still get the line in the same situation, it's got to be the monitor that's faulty - in that case it should still be under warranty, if your 8 months since you bought it is correct. There may be a local place where you live that is certified to repair Acer monitors - if not , you may need to obtain a RMA number or similar on the Acer site and have to ship somewhere at your own expense.