For those who still can't get their Mac to work after following the 12 step process by RM9981 try the following that worked for me: Check Security & Privacy under System Preferences and go in the Privacy Tab. Make sure there are no more Symantec or Norton files with access in the "Full Disk Access" and "Files and Folders" sections. I still had two processes hiding there even after running the cleaning programs and removing system extensions. Also, as bbaale suggested, run the command systemextensionsctl reset even if there are 0 extensions left. For those of you who can't access Safe Mode and your Mac keeps rebooting into Recovery Mode, try clearing PRAM by pressing the power button and then press command-option-p-r. This should lead you to the login screen instead of Recovery Mode and from here you can restart your machine into Safe Mode and follow the steps to remove Symantec files and extensions. Hope this helps!