Internet wont work but modem is working

Hello,
My modem is working fine but the internet is not workin for my computer. when i plugged the ethernet cable into my xbox 360 and went onto xbox live, it worked fine. so the problem must be with the ethernet port. my buddie told me to update it but i wouldnt get past properties. does anyone know how to solve this problem. The modem works fine but the computer says that its not attached.