I'm sorry to hear that you're having this issue.
That's a new one to me, and I'm not sure what the cause would be. I'd have to recommend having a service technician come out and inspect the unit. Unfortunately, I just don't have a diagnosis to offer.
I recently bought this tv from a friend.
I've got it home and it all works fine apart from this mark on the screen.
It is always there and always black.
Here are two pictures below
I have never seen this on an LCD before.
Any suggestions as to what it is or can it be fixed without changing the whole screen?
Thanks in advanced