WIFI doesn't work after a fresh 4.0 install

[firenice03]

Couple of things might be worth a try..


1st may a restore point with TimeShift - should something go south you'll have a fall back.. Then another after you find resolution.
The following shouldn't bother the system but never hurts..


Try disabling Bluetooth - sometime BT has been known to cause WiFi issues. Verify..


Since it worked in LL3.8, may be kernel related - LL3.8 ships with Kernel: 4.4.0-112 whereas LL4.0 ships with Kernel: 4.15.0-22
You can use Lite Tweaks - Kernel Installer;  choose 4.4 at least to start with..

• Click the radio button next to the version, click install then reboot
  
• At GRUB make sure you select the 4.4 version, verify if WiFi is working
  
• Can use Lite Tweaks > Kernel Removal to remove 4.15 or any other kernels not logged into
  

The above are easily remedied to go back to the original system. Reboot select kernel 4.15 from GRUB, use kernel remover from Lite Tweaks to remove 4.4 (Cannot be logged into the kernel you wish to remove)


The following I wouldn't attempt without having a restore - it'll be easier to restore versus removing..
Depending on WiFi encryption: https://ubuntuforums.org/showthread.php?t=2347479