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.
Because you've changed some settings in the router, the "profile" may 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 - 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:
If you're using Windows "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 "Remove" an existing profile click here
If you're using third-party software provided with the wireless adapter, there should be a similar option to remove an existing profile.