Do you get any error message, and does repairing the network connection solve the issue? Also, what's the network setup - is it just a PC wired to a router?
I also encountered this problem while installing this motherboard in a friend's computer. We were able to configure the speed of the NIC in the device manager to 10mb full-duplex and it was able to recognize the network... Strange that when it was auto-negotiate it wasn't able to do it. Physically setting the speed was the only way to get it to work... Very irritating.