You have link lights on the network card? If you go to Network properties does the connection show as connected?
Go to Start > Run, type in CMD hit Enter. Type in ipconfig, hit Enter. What do you get for a result? Is it a 192.168.1.x address or a 169.x.x.x?
Have you tried a different network port on the modem? Is it a modem or a Router you are connected to? Try to do a power cycle on it?
I did the ipconfig and got a 169.x.x.x.. what does it mean?! I am having the same issue..