The reason: sa account has not been granted permission to connect to the database engine, logon rights has also been mercilessly deprived.
solution:
After 1) windows log on, find: Security -> login -> sa, then right-click and select Properties.
2) Select General (Enter the new password, cancel the password policy).
3) Select the state (set granted and enabled).
4) Select the 
Right Properties - Select Security ( SQL Server and windows authentication mode) -> OK
5) Reboot the server