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Login in SQLPLUS with SYS as SYSDBA

C:\WINDOWS\system32>where sqlplus
C:\oracle\product\11.2.0\client_1\bin\sqlplus.exe
C:\oracle\product\11.2.0\dbhome_1\BIN\sqlplus.exe

C:\WINDOWS\system32>C:\oracle\product\11.2.0\dbhome_1\BIN\sqlplus.exe / as sysdba

SQL*Plus: Release 11.2.0.4.0 Production on Fri Mar 4 11:15:30 2016

Copyright (c) 1982, 2013, Oracle.  All rights reserved
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning option
SQL>

Confirm that DB is in NOARCHIVELOG
SQL> SELECT LOG_MODE FROM SYS.V$DATABASE;
LOG_MODE
------------
NOARCHIVELOG
Stop the DB
SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.

Startup mount and alter the DB

SQL> startup mount
ORACLE instance started.
Total System Global Area  184549376 bytes
Fixed Size                  1300928 bytes
Variable Size             157820480 bytes
Database Buffers           25165824 bytes
Redo Buffers                 262144 bytes
Database mounted.

SQL> alter database archivelog;
Database altered.
Open the DB
SQL> alter database open;
Database altered.