lost wireless connection on laptop

My son had his Dell laptop at college and was using their wireless network successfully. He came home last week and tried using his laptop on our home wireless network (w/Linksys router). He said he was not able to always connect so he tried to set up (configure, repair) the wireless connection himself (always a dangerous thing to do).
Now he gets no internet at all (IE always goes into 'offline' mode) under Windows XP home.

I've tried to trouble shoot the connection but so far I have been unsuccessful.
The laptop can see the wireless network (it shows as available and connected).
There is something wrong with the network connection that IE uses but I don't know how to go about fixing it.

In the laptop's Network Connections I see 'Lan or High-Speed Connections' with a 'Wireless Network Connection' of connected,firewalled. Also, in the configuration area under connection properties there is (checked) Client for Microsoft Networks, File and Printer Sharing, QoS Packet Scheduler, and TCP/IP. There are other services unchecked such as Client Service for Netware, NW Link IPX/SPX, NW Link Net Bios, AEGIS Protocol, WLAN Trans... (some/all of these I'm thinking were added for his university connection).

Can someone please help me. What can I do?

Thanks,
Walter