dark spot at the bottom of my screen

Hello All,

 

I have my 600M for less than 6 months, and I noticed that there is a dark spot coming up from the bottom of my screen. I know the light source is from the bottom and I wonder if some of the cells are burning out.

 

Has anyone experienced that? What is the reason for that? And how to fix this problem?

 

Any help will be very much appreciated.