I have the same problem with an ASUS G35 board that was sent back to me by ASUS support as a result of an RMA of my original board. The replacement works fine except the onboard Realtek LAN does not show up in Device Manager at all. The board was flashed with the very latest BIOS, so I haven't done anything there. After a lot of troubleshooting, I decided to keep the board and installed a third party PCI LAN card. Currently I use a wireless adapter with the board to log on to the interwibble.