Well, it sounds like a Hardware-Display Issue where the pixels died.
You might wanna use it until his birthday and adress the issue at your dealer. While you discuss with him the steps and what to do, you have time to still use it.
I would bring/ship the old one, as soon as i get the new one so you always have a "laptop", if you cant live a few days without it.
I guess nothing that the community can do here. Maybe some Programs to check for dead pixels