my acer a500 top of screen doesn' t work

I have a a500 tablet suddenly the very top of the screen doesn't respond to touch. I have to constantly rotate the screen when using it. 

I have had this tablet for a year. I had to send it back to acer to have power button replaced.

I have searched the internet for answers. Unable to find anything like this.

any help will be greatfully appreciated.

I use it in my job.