I believe it is a crossover cable, what is your network setup?
Mine is Router (Downstairs), PC (Downstairs, connected via ethernet to router), PC (Upstairs, connected via Wi-fi to router), Xbox 360 (Next to upstairs PC, connected to PC via provided ethernet cable and using PC's wireless connection to connect to router).
You need to set up connection bridging for this to work correctly.
Mine is Router (Downstairs), PC (Downstairs, connected via ethernet to router), PC (Upstairs, connected via Wi-fi to router), Xbox 360 (Next to upstairs PC, connected to PC via provided ethernet cable and using PC's wireless connection to connect to router).
You need to set up connection bridging for this to work correctly.