unable to find wireless network

My grandson has a computer with a wireless card installed and was running
well to the local router in his house. There was a problem with 2 cards
suddenly conflicting with each other so I removed all of the cards and
replaced them one at a time. Now the conflict is gone but the wireless card
does not find the access point anymore. I tried 3 different types of
wireless card and all of them do the same thing. It says " One or more
wireless networks are available" but when he brings up the connection
dialog, it says there are none available. I know the wireless network is
available because I can take my laptop to his house and connect right up.

Any suggestions as to what to try next??

TIA