When you connect to a wireless network, a "profile" is saved so that, in future, the Wireless Network Adapter will connect automatically to the network if it is available.

If you've changed some settings in the router, the "profile" will no longer be valid and so you cannot connect. You need to delete the existing "profile" and then go through the procedure to "Connect" again when a new "profile" will be created - in other words, run the wireless adapter's software, scan for "Available Wireless Networks", find and highlight the one that matches your router's SSID (network name) and select the option to "Connect" to it. You should be prompted to enter any WEP or WPA encryption key and, once "Connected", the wireless adapter should get its IP address by DHCP from the router and you should have network and internet access.

To delete the profile:
In Windows XP, if you're using "Wireless Zero Configuration" to manage your wireless networking, go into the Network Connections folder ("Start > Run", type ncpa.cpl and click OK), right click the Wireless Network Connection, select Properties and then the Wireless Networks tab, where you can highlight and then "Remove" an existing profile.



If you're using third-party software provided with the wireless adapter, there should be a similar option to remove an existing profile.

In Vista, right click "Network" (My Network Places) and select Properties. Click the link at the left to "Manage Wireless Networks" then, in the next window, highlight the "Network" to delete and click the "Remove" button.