I'm going to guess that Ubuntu isn't distributing firmware for the bcm43xx driver (the native Linux driver). Have a look in /lib/firmware, and if there isn't one, or if it is empty, you're going to need to create the firmware.
That you do in a few steps. First, download and compile fwcutter
. Then you need to get a Windows driver to extract firmware from. The file wl_apsta.o
is highly recommended. You then need to run fwcutter against the driver to extract the fimware and finally, you need to copy it to /lib/firmware. All of this is the README that comes wtih fwcutter as well.
If that was the problem, you should be able to remove and then reload the bcm43xx driver and hopefully that will get it functioning. You'll still have to configure it and set up wpa_supplicant, but firmware is the likely first step.