I was working on setting up 10 HP Compaq nc6400 laptops and one would not allow the wireless button to light up in blue. The driver was installed, but it didn’t show any networks in range.
My fix was to press F10 as soon as I turned on the computer, went the the System Configuration menu, Built-In Device Options, and I changed Embedded WLAN Device Radio from Enable to Disable (use the arrows)*. Hit F10, then ESC, Save Changes and Exit. I booted into Windows, shut down, then went in to change it back to Enable. Once I got back to Windows it worked!
*If your setting is set to Disable, set it to Enable and it should fix your problem.