Did the wireless card ever work on your network (allow you to connect to internet)?
What are you running XP, Vista...?
If XP, in lower right corner, right click on the 2 computer icon that show you connected. In the pop up you will see Open Network Connections.
You should see a "Wireless" Network connection with a status of enabled. Note the name of the connection.
Right click on the connection and disable.
Reboot machine - Shut down restart
When re logged on, you will not see the connection in lower right as you have disabled it.
Go to START >>> SETTINGS >>>> CONTROL PANEL >>>> NETWORK CONNECTIONS.
Find the connection you disabled, right click on it and ENABLE the connection.
It will search for an IP and connect.
If you are still having the problem, you should still reboot your router and modem. Sometime the IP address assignment from the router get's conflicts (if you don't hard code them at set up) with multiple wireless devices
I'm only on PC early in a.m. Lots of yard work happening. Let me know if it worked for you.