Hi , I am Dexter, an Independent Advisor, here to help you.
Does this line look like from the pic I attached(It's vertical in the pic)?
If so, there's a hardware problem with your monitor, probably the LCD screen is damaged, so you should have your monitor repair or replace.
I hope this helps. Feel free to ask back any questions and let me know how it goes. I will keep working with you until it's resolved.