HELP WITH AIRPORT EXTREME - NO WIFI

I have DHL, a new Airport Extreme, 4 apple TV boxes, 3 Apple computers, 2 iPhones, and my sons Alienware Laptop. the problem is that since I purchased the new Airport Extreme Two apple TVs and My sons Computer cannot connect to the internet.

I have rest both router and modem. I have reset computer and apple TVs.... ANy Ideas?