1. Open cmd, input: sqlplus
2. input: /as sysdba(logon as system administrator)
3. input: conn sys/sys as sysdba(sys is a demo database of Oracle)
4. input: alter user scott account unlock(unlock scott account, the original status is "lock", PS: scott is a user exists in Oracle demo database)
5. Now you can manage the demo database using scott user, input: conn scott/tiger(tiger is the default password for scott)
Please refer the p_w_picpath below for detail: