Got so start--control panel---network connections

Make sure that your Wireless connection is enabled. If it is then right click on it and select properties.

Now do you have you router set up to be a DHCP server, or do you assign your IP's statically?

If it's DHCP make sure that under TCP/IP then properties, that the obtain and IP automatically is checked. If you assign your IP's staticalyy then make sure your subnet and gateway information are correct.