You can also check to see what if any security has been enabled on the access point. If MAC address security has been enabled, and you have not added the MAC address of the device you're trying to connect with to the access point/router - you will not get an IP address, even if you have the correct wep/wpa/etc. password and can connect to it.
In addition you can try disabling IPv6 in the properties of the network card (or wireless card) you're trying to connect with.