Hello,
First of all i apologize about my english (i´m from Spain).
I have just bought a GA-x58a-ud3r Rev2.0 and i have the same problem with ethernet port. I have seen other forums and people have the same problem. I update all the drivers on my Windows 7 64bit, Linux... I update the bios (FF)....
Ethernet is working sometimes, but i think if i restart the computer ehternet dies. If i shut down, wait a minute, and power on, it alives again.
May be it can be solved with a new bios update?
I had got another GA-x58 ud3r Rev1 and it hasnt this issue. And i had a H55n-usb3, its great.