Dell Ultrasharp LCD problem

[Andy74]

I have a small problem with the DELL Ultrasharp LCD (18.1). There is an uneven black shadow at the bottom of the display, it's getting bigger every day. Any ideas what migh be causing this?
The display is about 2 years old

Plese see the attached link.

Thanks, Andy

Clik to see the image

 

[Andy74]

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