Macbook Pro , OSX 10.5.8: Airport constantly scans, shows no SSID's

Gentlemen,

I haven't been able to find out what may have happened to this machine, which is causing it to not be able to show or see any nearby wifi routers.

Right clicking on the Airport icon at the top menu bar, shows:
AirPort: Scanning ... or AirPort: ON (grey)
Turn AirPort Off (black)
------------------------
No network selected
------------------------
Join Other Network... (black)
Create Network... (black)
Open Network Preferences... (black)


One problem is the status of the AirPort is always scanning.


Clicking on Open Network Preferences
Location: Automatic

Services on left side are:
  Bluetooth (status=red, not connected)
  Ethernet (status=red, not connected)
  FireWire (status=red, not connected)
  Airport (status=Yellow, On)

Status: On [button: Turn Airport Off]  "AirPort is turned on but is not connected to a network"

Network Name: No network selected
clicking on the up down arrow shows:
  + No network selected (grey)
  -------
  Join Other Network... (black)
  Create Network... (black)


Clicking on Join Other Network shows a popup box
  Network Name: have manually typed in the name of the customer network
  Security: None (for the sake of testing, I have disabled encryption)
  Remember this network: No (for testing)
After clicking on the [Join] button, error text is shown "Connection failed"

Click on [Show Networks] button, a popup box is displayed saying "Select the network you want to join".
This list is empty.  


My question: How to enable the showing of nearby wireless networks, to choose one of those networks, and connect to it.