ORA-01033: ORACLE initialization or shutdown in progress

When I tried to connect to DB via SQLPLUS i got the below error

C:\Users\USER>sqlplus

SQL*Plus: Release 12.1.0.2.0 Production on Sun Feb 28 14:12:46 2016

Copyright (c) 1982, 2014, Oracle.  All rights reserved.

Enter user-name: userdb
Enter password:
ERROR:
ORA-01033: ORACLE initialization or shutdown in progress
Process ID: 0
Session ID: 0 Serial number: 0

Try the following commands:

c:\>sqlplus /nolog

SQL> connect sys as sysdba

SQL> alter pluggable database all open;