How can I connect my itunes account to my Apple TV Generation 3 device?

Just bought a Generation 3 Apple TV device off ebay. I now have the device setup with my tv and is also connected to my home wifi, however when I enter my itunes email and password, it will say it's either incorrect or cannot connect? I've tried entering it so many times, I've gone through my itunes account settings, my phone settings etc and still nothing. How can I connect my account to the apple tv device?