Windows7 won't get IP from Mac10.8.2 DHCP server

Hey.

I just discovered a very big problem. I bought me a powerline adapter to share internet from my mac mini server to my friend's windows via lan and to connect the two on a fast speed. Now the problem is that the windows system is NOT getting any IP! Running 'ipconfig /renew' returns "The data was invaild". The MacBook Air though does recive an IP. What is going wrong here? I really need to know a fix!