Comment 11 for bug 1777646

Here is what worked for me to restore WiFi functionality...

1. Run Software & Udpates from the launcher. In the Developer Options tab, check the box for Pre-released updates. This will require your admin password and will update the cache.

2. Run Software Updater from the launcher. It will present you with lots of options of stuff to update. Because I did not want to beta test the whole proposed release at this moment, but just fix my WiFi, I unchecked all of the updates except the Broadcom wireless driver. Then I installed this update, which did not require a reboot.

3. I tested the WiFi by unplugging the internet cable and connecting to wireless, which worked. A reboot was not requested so I didn't reboot.

4. Run Software & Udpates from the launcher. In the Developer Options tab, uncheck the box for Pre-released updates. This will require your admin password, again. It will update the cache. I did this because I don't want to install any further updates from the Proposed (pre-release) repository, just the one I needed to make WiFi work again.

My computer is a very old Dell Inspiron with Ubuntu 16.04. The wireless was working until I updated the OS this morning and the update failed due to a Broadcom driver problem, as described in this post and also here: https://bugs.launchpad.net/ubuntu/+source/bcmwl/+bug/1757008. The above procedure corrected the problem without introducing any new problems. Thanks to everyone who contributed the fix! Much appreciated.