Connected but can't connect to anything

My partner is running Kubuntu 12.04 (as I also am) on a laptop with a wireless connection. The networking icon on the bottom row indicates that her laptop is, indeed, connected, as does System Settings / Network Connections / Wireless. Nevertheless, she isn't able to connect to anything, either through Firefox or by pinging. What might account for that? I'm trying to talk her through this over the phone.

Maybe there is no DHCP server, hence you can connect to the WiFi, but to use the actual network you need to supply a valid TCP/IP address and appropriate entries for gateway and DNS server on your own. The chosen address for this machine must fall of course in the address range provided by the WiFi network.