If you run into a problem where the hitting the Windows start button and the menu doesn’t pop open then it can be a corrupt profile.
I would backing up the user data before you start this process. This is the “C:\Users\” and that user’s folder.
Open the control panel, go to “User Accounts”, “Manage User Accounts”, and remove a user. You will need Administrative privileges to do this. Make sure when doing this to delete all files so that nothing is left. Then re-create the user and verify once you are logged in that things have returned to normal.
This start menu issue that we resolved this was was only affecting the end user not the whole OS, so it was a profile corruption problem.