Most of the users are tackling problems with Cortana and the Start menu not launching. Every time a launch is attempted, users see a “Critical Error” message saying that the functions are not working and a fix will be attempted the next time the user signs in. Workarounds, such as rebooting or refreshing the system, making a new account, or using other accounts, have all failed for a majority of people who upgraded to Windows 10. “So Installed Windows early this morning and once I was able to log in onto my personal account. I got a pop up saying ‘Critical Error Start Menu and Cortana aren’t working. We’ll try to fix it the next time you sign in.’ I read online to try a different account. I have tried that with numerous accounts and I still have the problem,” complained a user who upgraded from Windows 8.1 to Windows 10 on the Microsoft Forum. Another user also shared: “Upgraded my system yesterday and it was working well until an hour ago. I decided to restart my system and after that, the problem occurred to me as well. Please help. I need it to be fixed as soon as possible.” Some users even attempted to go back to their older OS to resolve the issue but to no avail. Now a redditor, Xeasar has found that the reason for the critical issues with Task Bar and Cortana are due to some compatibility issue with Avast Anti-virus. He found that once he uninstalled the Avast anti-virus software from his Windows 10 PC, the computer worked normally. According to Xeasar, Microsoft is aware of the cause of this issue and is working on a patch.