Why is my airport extreme not logging on to my network
My AirPort Extreme not logging on to my network.
Instead it uses its default IP address to connect.
But then I cannot used the Internet
Disconnect the cable going to your cable modem (router) on the AirPort.
Now reset your cable modem so it gets a fresh DHCP address lease from your ISP.
Then using your Mac or iOS device open the AirPort Utility and do a reset while its resetting quickly plug it back into the modem so its DHCP lease is renewed as well. Once restarted that should have fixed things. The AirPort LED should be green now.
If not try replacing the Ethernet cable between them as it maybe bad or damaged.