Macbook WiFi card not working I have a Macbook 1.83ghz. 

I installed Snow Leopard and the WiFi crashed (?) 

It was barely functioning before, but now all it can do is detect names of routers.

I haven't done anything as I don't know what to do. 

How do i run a diagnostic before I have to buy a new WiFi card?
Lets do some information collecting then do some testing.


  Click on the Apple (top left)
  
  About this Mac
  
  More Info
  
  System Report
  
  Now look for Network and WiFi


There you will see the information about your WiFi card and the status of the connections.

It looks like this:


As next step I suggest to do some Diagnostics.

Than open the Network Diagnostics to test your WiFi connection.


  Choose Apple menu > System Preferences, and then click Network.
  
  Click “Assist me,” click Diagnostics, and then follow the onscreen
  instructions.


This test will tell you about your WiFi card and connections.