Can you run the following commands one after the other.
sudo modprobe -r wl
sudo modprobe b43 allhwsupport=1
That should switch wifi on. To make it permanent open /etc/modules-load.d/modules.conf and add b43 underneath:
# List of modules to load at boot
b43
Now open /etc/modprobe.d folder and create empty document and name it b43.conf, open it and make it look like this:
options b43 allhwsupport=1
Reboot and it should work.