I have changed my NIC's MAC because the original MAC is illegal
How is that possible? By definition, a MAC address can't be illegal, as it is wrote physically in your network card "chipset". It is very unlikely to be filtered by some kind of firewall too, as MAC address is way way harder to spoof than ip (and since it is a "physical" address, you can't just filter your clients MAC).
Anyways, once you "spoofed" your MAC address, your gateway/router will no longer recongnize you, as his ARP table will be wrong, you will have, at least, to call back the DHCP...
Still, this is... suspect?