Random Computer/Internet Question

Whenever my friend visits from college, he can't get his computer to hook up to my internet. I know the cord works, and all my computers will hook up just fine. His (laptop) computer, however, will not, even though he can use the wireless connection at home and the ethernet cord connection at school. I have the cord connection. Nothing is wrong with the cord. Enabling/disabling the wireless switch does not seem to change anything as far as his ability to connect to my internet. The computer recognizes the connection but won't connect. I have Comcast "high speed" internet but I have no idea whether it's cable or dsl (I might be able to find out soon, but the person who handles our computers has an away message up at the moment). Does anyone have any idea what could be the problem and how such a computer might be able to connect to the internet? I am looking for as many possibilities as possible, though the boy who handles this stuff for us could eventually come out if everything fails. (Also, the computer is not here at my house with me right now; this is for future reference because it's always a problem).