Please run ipconfig/all from a cmd line prompt. Your output should include some details that include the Physical Address of your network connection. Here is a sample:
Ethernet adapter Local Area Connection:
Connection-specific DNS Suffix . : subdomain.domain.com
Description . . . . . . . . . . . : Intel(R) 82566DC-2 Gigabit Network Conne
Physical Address. . . . . . . . . : 00-1C-25-9B-48-1F
What is your physical address? Do you get all zeroes for your physical address? I am asking because the Intel(R) 82566DC-2 Gigabit Network Connection uses the same driver as the Intel(R) PRO/1000 PL Network Connection. If you get all zeroes, then the solution can be found in Did your Intel® PRO/1000 PL Network Connection Stop Working after a Driver Update? As far as I know, all the reports were limited to the Intel(R) PRO/1000 PL Network Connection, but maybe this might have happened on some other connections that I did not know about.
I assume that everything was working correctly before the clean OS install. You might want to try uninstalling the network connections driver and software and installing an older version to see if the problem disappears. The version 14.6 software package, PROEM64T.exe, is still available in Download Center and has an older base driver that might work differently with your desktop board.
I hope this helps. Let me know what you find.