iMac 27 cannot attach to Airport
My machine is an iMac 27, Late 2012 running OS X 10.9.4 Mavericks. This evening, out of the blue, I lost Internet connection, and had an alert come up for a Thunderbolt Bridge. I'm aware of what the Bridge is, and I've already disabled it. But I am still unable to get my iMac back online. The Airport is up, connected, running the latest firmware, and is providing Internet connection to both this iPad and to a second, identical iMac 27. I have restarted the affected machine multiple times, but nothing is working, and there is no error message to give me any idea of what to do next.
How do I get this system connected again?
iMac, OS X Mavericks (10.9.4)