I have just run into a similar problem while installing Mint17 on a Dell Latitude D505. After many false starts I found the recommendations in http://askubuntu.com/questions/45912...-14-04-install
, with a modification for the BCM4306 V2 device:
sudo apt-get purge bcmwl-kernel-source
sudo apt-get update
sudo apt-get install firmware-b43legacy-installer
shutdown computer; unplug network; restart; Wifi should work now.
If you have a different Broadcom card, see https://help.ubuntu.com/community/Wi...Driver/bcm43xx
I think the key is the purge command, because it also fixes the configuration files.