What is displayed on the screen is a representation of what is in memory.
While it might be your screen, you could also have a memory (RAM) problem.
This link will take you to a MemTest -
MemTest download and review - RAM reliability tester from SnapFiles.
Follow the instructions.
Run it for at least 24 hours. The longer the better.
You can continue to use your computer while it's running.
If there is not problem, then it will just continue to run until you stop it.