A friend has a Mac book Pro which had wireless Internet working, but then worked intermittently, and now not at all.  The modem still works using an ethernet cable.
 

when attempting to connect the message is : "You are not connected to the Internet" and "connection time out occurred".  

I know nothing of Macs so don't know even where to begin.  I wondered if she needs to enter the encryption key and password into the Mac wifi settings.

any ideas or guidance greatly appreciated.

Thanks