Before you do anything drastic, try connecting the AVR to a different port on the router or switch. I received a call from a customer who lost two TVs during the Summer and now that Winter is here, they want to use them. After I determined the problem was two dead TVs, they bought new ones and when I returned, I found that the AVR was outputting no video. I also found that its network card still worked, but the Access Point in the garage didn't, so I connected a different AP. That didn't work either, so I used a different port and it returned to normal.
These aren't the same as computers, which often have a network card that's separate from everything else- if you have been using WiFi, try it with an ethernet cable. No MAC address does indicate a bad NIC, but remember, the wireless may use a separate one.