Have you tried it with WEP disabled on the router? Turning it off for a few minutes and try with your laptop.
If that works try the suggestions from this page:
first find out the name of your adapter note the adapter that has wireless extensions and do these steps substituting eth2 with the adapter from above and your essid name and key
If this works then try again with Network Manager
sudo iwconfig eth2 essid yournetworkname
sudo iwconfig eth2 key yourwepkey
sudo ifconfig eth2 up
sudo dhclient3 eth2
unlock using your password and enter the settings.
If this goes well think about changing your network fromm WEP to WPA-PSK