Hi. My name is*****'m a camera repair technician with over 20 years in the business and I'll be glad to help you with your question today.
The most common reason for this is a bad LCD Flex Cable that connects the monitor to the camera body. These are looped through the hinge assembly and take a lot of abuse. They go bad all the time. You may want to check locally for a camera repair shop in your area, or, if you need assistance finding a shop, please let me know and I'll locate one for you.