If it Matters I upgraded to Windows 10 from 8.1 on my Old PC, and my Newer one, and didn't experience any problems with it, though I let Windows Defender run during upgrade install, then did a clean install following the upgrade, did all the WIndows 10 updates, then configured Avast Free again, no issues with Start menu, Cortana at all, been running this System almost a month now, Sleep and Restarted off and on.
refreshed my old system and gave it to Mom, again no issues experienced with Windows 10 or Avast once I got Avast installed
My Theory is could be a conflict with someones start up item, a setting, or something