TV shows only a thin horizontal light whenever i...

Question

Please Help!!!My TV screen remains like it is still switched off whenever I switch it on, with the exception of a bright horizontal light across the middle of the screen.It started about a week ago. it wasn't that serious at first. once in a while the picture would shrink a bit towards the center( making the picture look wide) and become darker. Picture would also become a bit shaky. It usually returned to normal after a while or when I hit the TV.