I can only *assume* you need to restore your device. Does it possibly have water damage? Did you drop it? Is it jailbroken? In any case, I recommend you connect it to iTunes, back it up, and then restore it and set it up as a NEW device. After the process is complete, check to see if the screen is performing as it should. If it is, go ahead and set up your device for use. If it does not, you may need to make a Genius Bar appointment with the nearest Apple Store and have them diagnose the problem for you.