yes nvidia is right the lan is MCP integrated NVIDIA® MAC + Realtek® 8201BL PHY....
1) this wouldn't be an issue of turning it on in bios if its already detected and installed
2) check for the latest bios or updated drivers here
http://www.asus.com.tw/support/downl...odelName=A7N8X make sure your looking for the right board there are several revisions of this board
3) you said the other on worked just fine can you elaborate on what your connecting to ?? I'm assuming a router or ext modem
are there also realtek drivers on the cd try those or check the realtek webiste for updated drivers