I have a Dell Inspiron 1521 which is about 2 years old. 6 months back a column about 3 inches wide began to darken on the left side of my screen. I had the LCD replaced and eventually the same problem occurred again on the new LCD. The problem seems to be linked to how long the laptop has been running and whether the power adaptor is plugged in or not. When I start the machine after it has been off for a while, there is no problem initially. However, eventually the dark column will appear. Also, the dark column only seems to appear if the power adaptor is plugged in. If the machine is simply running from the battery, no dark column will appear. I have no idea why this happens, so any suggestions would be much appreciated.