Power off both your Mac and the AirPort Extreme
Wait a minute or two and power up the AirPort Extreme first and let it run a full minute
Then power up your Mac
See if that helps
If still no luck, temporarily connect an Ethernet cable from your Mac to one of the LAN <-> ports on the AirPort Extreme and try that way
At this point, unfortunately your options are limited.
If you have an iPhone or iPad with AirPort Utility installed, you should be able to use that device to administer the AirPort Extreme....assuming that the Extreme is functioning correctly.
Otherwise, your only other option is to perform a factory default reset on the AirPort Exteme to get it back to original settings, then configure it again.
But...if the AirPort Extreme is having problems, there is no guarantee that this will work. The A1143 model is probably 5+ years old. I got about 4 out of my old A1143.
Post back if you want to try the factory default reset on the AirPort Extreme.