I was setting up my mum with her new laptop and had something similar to what you describe, one laptop was working fine, (although I was unable to access any of the settings on that) and hers that wasn't. It said the signal strenth was excellent and when I typed in what I thought the key was for the wifi it would sit there telling me it was acquiring the IP address, and then wouldn't connect.

Eventually after an age I was contacted by the guy who had set up the wifi and he gave me the correct key, which he had changed. So it might be worth trying as is mentioned above deleting and then re entering all the connection details. Oh and make sure you use the correct WEP/WPA/WPA2 etc.