You might try clicking Connect To (or Control Panel, Network Connections) Show All Connections, then select the appropriate connection, go to Properties, TCP/IP properties and make sure that IP address is obtained automatically and that DNS server address is obtained automatically.

While you're at it make sure Firewalls are Off (Windows' firewall is under Advanced properties) until you get a reliable connection.

If using wireless and you know how to address the router, also turn off wireless security until you have a reliable connection.