You're right, if the wired ports are working, the wireless should be working. Are you using a static IP on the PC's connected to the wired ports, but DHCP on the wireless? If that's the case, the DCHP server would assign its IP address (the IP address of the second router) as the DNS server. Just a guess. Try connecting to the second router wirelessly, then enter an external IP address (Google's is 72.14.203.99) in the address bar. If you get Google, go into the second router's setup and disable the DHCP server.