click start > settings > control panel.
Find and double click on network connections, look for a connection named "local area connection" and right click on it. select properties. on the network connection properties look for internet protocal( TCP/IP) and double click on it.
Then make sure that both the tick boxes labeled obtain IP address automatically and obtain DNS server address automatically have got ticks in them
Click ok a few times, wait a minute or two and try again.