Article : Ubuntu_wifi_not_working_anymore

if the Switch for wifi is set to off :

# rfkill list all # Check for Devices which are switched off

# rfkill unblock all # Turn it on again...

# rfkill list all # Show the new State...


if Wifi is activated, but no new Connections are possible...

# sudo apt-get install linux linux-headers-generic kernel-package # I installed it already...
# sudo apt-get install --reinstall bcmwl* firmware-b43-lpphy-installer b43-fwcutter # Reinstall alle the wifi Drivers for The Broadcom Wifi Card
# sudo reboot # Finaly reboot your Computer

If that didn't help, try these commands:

# sudo apt-get remove bcmwl-kernel-source
# sudo apt-get install firmware-b43-installer b43-fwcutter
# sudo reboot