I received an Inspiron 15R 5521 last year for my birthday, and a few weeks in, it developed a white vertical dead pixel line. This happened without dropping it or being rough with it. Over time, the dead pixel line would disappear and reappear, until one day it was there permanently. Now, there are over ten dead pixel lines claiming a horizontal centimeter in vertical white pixel lines. I have never dropped it or been rough with my laptop, so why do I have these lines, does my warranty cover it, and how do I fix it?