Ubuntu 16.04 - only connecting to ethernet, no wifi option

modprobe: ERROR: could not insert 'wl': Required key not available

This is the subject of a recent and still open bug in Ubuntu: https://bugs.launchpad.net/ubuntu/+source/bcmwl/+bug/1572659

It appears that the only solution so far is to enter the computer's BIOS and turn off Secure Boot.

To do so roam around the options after booting your windows machine in F12 mode, until you find a Secure Boot switch and turn it off. Then exit and boot Ubuntu normally

Secure Boot is a security standard developed by the PC industry to help make sure that your PC boots using only software that is trusted by the PC manufacturer

Reboot. Your wireless should now be working.