I have a lap top and belkin wireless modem via cable broadband. Im not sure when I set this up that I added any security to stop other people using my connection. I've tryed a few times but always fail. anybody please help!
It's very easy, but without a model number, my instructions will have to be generic.
 Open Notepad and type out a long mix of upper- and lower-case letters, numbers, and symbols. Circa 20 characters. Paste it to the clipboard and save the document with an innocuous title.  Turn off any wireless clients. Access the router over an Ethernet connection. DO NOT access it over a wireless link or leave any wireless links active.  Log in to the router's configuration menu.  In the Wireless section, choose Security.  Select WPA-PSK or WPA2 or similar - not WEP - from the drop-down box.  Paste the key below.  Save and close. Reboot the router.  Take your text file to any and all wireless clients.  Browse for your SSID and attempt to connect. Paste the key twice, once on each line of the pop-up box. Connect.
The above assumes that you are using Windows' Wireless Zero Configuration and NOT any third-party adapter management software.
SSID???????????? Short for service set identifier, a 32-character unique identifier. The SSID differentiates one WLAN from another, so all access points and all devices attempting to connect to a specific WLAN must use the same SSID. A device will not be permitted to join the BSS unless it can provide the unique SSID