Open up "Network and Sharing Center", click on "Change Adapter Settings", then right-click on Properties of your wireless network adapter, then click on "Internet Protocol Version 4(TCP/IPv4)", then click the Properties button, and make sure you are set to "Obtain an IP address automatically", and "Obtain DNS server address automatically".
[EDIT] Sorry, I forgot that you already tried this. If you go into Network and Sharing Center and click on the "X" in the network diagram that shows you don't have Internet connectivity, Windows should try to troubleshoot your problem and may give you some useful information.