Check this link Broadcom STA Wireless Driver for the initial help. It has instructions on how to determine your card model and how to install if you have an internet connection or not.
If that doesn't get you anywhere, try this. I found this on a forum somewhere (credit to whoever wrote this):
Please try the b43 driver and firmware instead of the wl driver.
Please copy-paste the following commands into the Terminal (using a working, wired Internet connection):
sudo apt-get update
sudo apt-get remove --purge bcmwl-kernel-source
sudo apt-get install firmware-b43-lpphy-installer
Then please run the following command:
gksudo gedit /etc/modprobe.d/blacklist.conf
Using the gedit editor, please REMOVE the following configuration lines in
Save the change to the
/etc/modprobe.d/blacklist.conf file after removing the
Then reboot and retest wireless.