The best thing to do is buy an ethernet card and plug it in.
OR replace the motherboard with some other type.
You are describing the "classic" asus defect.
Once I flashed a bios update on an expensive ASUS board, and somehow the MAC Address of the onboard LAN got zeroed. Worse yet, somehow when you plug in an external LAN, that MAC Address is also not recognized until the onboard was disabled in the BIOS. This was very frustrating.
RMA'd with ASUS, and ASUS sent me back a board badly damaged during transit because they did not wrap the board, just tossed it in a paper box.
Then RMA'd with ASUS again, they tried denying warranty, and finally relented and sent me a dusty looking old board. That board died 3 months outside of warranty...
END Off Topic.