Driver from lspci: Broadcom Corporation BCM4321 802.11a/b/g/n (rev 03)
On Ubuntu, you will need headers and tools. Try these commands:
sudo apt-get install build-essential linux-headers-generic
sudo apt-get build-dep linux
sudo apt-get update
sudo apt-get –reinstall install bcmwl-kernel-source
Reboot and try it out!
Source:http://www.broadcom.com/docs/linux_sta/README.txt