I know for a fact that Avast is the cause of Cortana not working. I do computer repair for a living and none of your solutions work when Avast is installed on Windows 10, the only way I have found after hours of trying was to remove avast and just not use it on a Windows 10 system. I have had probably 20 fresh install Windows 10 systems with this problem all with Avast installed and the only solution was to remove Avast. So now instead of every computer that comes through my office getting a free copy of Avast they just use Windows Defender. Way to not own up and continue to loose customers. You can't tell me that when I have probably done 100+ Windows 10 systems since launch day and none of them have had this issues unless Avast was installed that its a Windows problem. If Avast is the only common denominator then that's probably the problem, no problems on any of my customers computer since I stopped installing Avast. I am truly disappointed with Avast for not owning up and fixing the issues with their software.