Lenovo b570 Broadcom Corporation BCM4313 wireless doesn't work
I have the same wireless card on a Lenovo U160 and I got it working by
gksu gedit /etc/modprobe.d/blacklist.conf
and adding
blacklist acer_wmi
to to the end of the file. Restart your computer and hopefully your wireless works. Maybe you have to press Fn+F5 (the wireless activation key combination) once or twice, but for me it just worked instantly after rebooting.