Has the TV been exposed to ANY sort of moisture? Damp atmosphere? Try covering the TV in a cotton blanket over night. This can sometimes draw the moisture out. If there is a no to both of these, then see if anything happens when you press the screen BEZEL around the side of the effected area. This will be a case of trial and error to isolate the problem. HOw old is the TV? And is it Plasma or LCD/LED