This solution is for specific problem only.
I have compaq presario laptop.
It happen with my pc that there is driver for my WiFi adapter, but after installing ubuntu the wifi button is not activating i.e. it remains red.
So I just restart computer then go to Microsoft Windows and ther I connect to the wifi.
Then without swiching off the wifi buttong i restart the computer.
Go to ubuntu then ubuntu automatically detects the hardware and my wifi is on.

Is your was the same problem?
Reply.