Dead Pixel and screen issues on HP EliteBook 8440p

It has been a month since I started using Elite Book 8440 p and now it is showing strange screen behavior. Some of the pixels do not perform as expected. This started to happen after prolong use of laptop so I would restart it and use it again. But once dead pixels appear in a particular session, even after restarting the defective pixels now appear more frequently than the first occurrence. Also, sometimes the screen brightness changes automatically and it becomes completely white than it changes back to the original brightness automatically. Why is this happening and what is the solution for this?
