|You need to encrypt your WLAN so as to prevent intrusion, hacking and your signal being used by others for nefarious purposes.|
Unless of course that is, you WANT the police knocking on your door warrant in hand so they can search through your computers to find the kiddy porn someone else has been downloading using your WLAN.
Once you've protected your WLAN using WPA encryption (WEP can be cracked in like, 10 minutes) then you'll need to join all your computers to the new WLAN. If you continue having problems with the same unit, get back to us here and we'll see if we can help you get it connected too.
One thing, attempt to connect that troublesome unit last.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.