Ubuntu 18.04: No WiFi adapter found - secure boot disabled

Lets first check the file system...

• boot to a Ubuntu Live DVD/USB
• open a terminal window
• type sudo fdisk -l
• identify the /dev/XXXX device name for your "Linux Filesystem"
• type sudo fsck -f /dev/XXXX # replacing XXXX with the number you found earlier
• repeat the fsck command if there were errors
• type reboot

Lets remove the incorrect drivers, and try and reinstall the firmware files...

sudo dkms remove rtlwifi-new/0.6 --all # remove incorrect dkms driver

sudo apt-get purge bcmwl-kernel-source # remove incorrect broadcom driver

sudo apt-get update # update the software database

sudo apt-get install --reinstall linux-firmware # reinstall firmware

reboot # reboot the computer

Recheck wireless operation.

Update #1:

Found hugely bloated Intel firmware at /lib/firmware/iwlwifi-8000C-34.ucode and /lib/firmware/iwlwifi-8000C-36.ucode. Removed them and reinstalled linux-firmware, and the code sizes look good now, but it still doesn't work.

Update #2:

Booting Fedora Live results in the same wireless errors that we see with Ubuntu. Suspect a problem with the wi-fi card. It may need re-seating or replacement.

This happened to me one time. It turns out I disabled Intel Platform Trust Technology in BIOS. Making sure that was enabled fixed my issue.