My macbookpro with Lion freezes when I attempt to turn WiFi on.

My 15" macbook pro freezes when I try to turn wifi on. This has happened recently. Initially I received a message that the hardware was not installed on the computer. Going through system preferences I 'started' the wifi but did not find any available networks. Following the first freeze the computer generated an error message sent to Apple - at that time I thought that it was something to do with accessing an external disc with a large aperture library but subsequently I realise that it is the wifi.

Help much appreciated.