i have the same problem, i've checked Intel connection advanced properties in the speed conection section where it says the speed:
Duplex 10 Mbps
Duplex 10 Mbps Complete
Duplex 100 Mbps
Duplex 100 Mbps Complete
1 Gbps
i am a venezuelan user, my Internet Service Provider has 100Mbps, but when i put specify 100Mbps Complete the network adapter shut down and says "Disconnected, Network Cable is Unplugged",change the connections, cables, and plugged direct with the modem and nothing, the network icon flash very fast "connected to disconnected" but without internet service, however when i put on 10Mbps Complete the internet connection works...but just on that speed, i really need help, my previous mobo works on 100Mbps,