Restart the database startup and report ORA-01031 insufficient privileges error solution

SQL> startup;

ORA-01031: insufficient privileges

SQL> conn / as sysdba

Connected to an idle instance.

SQL> startup mount; (starts the instance, but does not open the database)

ORACLE instance started.
Total System Global Area  285212672 bytes
Fixed Size                  1218968 bytes
Variable Size              88082024 bytes
Database Buffers          188743680 bytes
Redo Buffers                7168000 bytes
Database mounted.

SQL> alter database open; (After starting the instance, change the database to open)

Database altered.

SQL>shutdown immediate closes the database;

Database closed.
Database dismounted.
ORACLE instance shut down.

SQL> startup started normally.

ORACLE instance started.

Total System Global Area  285212672 bytes
Fixed Size                  1218968 bytes
Variable Size              88082024 bytes
Database Buffers          188743680 bytes
Redo Buffers                7168000 bytes
Database mounted.
Database opened.

SQL>