My Airport Extreme is installed & working with my MacBook Pro, iPad, & iPhone. Wireless signal is great. I now want to hook my old desktop PC to the router so I can access the internet from it. I bought an ethernet cable & plugged it in one of the 3 open ports on the back of the wireless router. I then connected it to the original port where the DSL cable connected before the new router was installed. I'm getting no connection now. Any help?