Oracle: unable to change to noarchivelog
ORA-12560: TNS:protocol adapter error on Windows is typically caused by incorrent ORACLE_HOME and ORACLE_SID environment variables.

Find the database service:



Find the path and name of the instance:



Based on that:

set ORACLE_HOME=O:\oracle\product\12.2.0\dbhome_1
set PATH=%ORACLE_HOME%\bin;%PATH%
set ORACLE_SID=RTG


Then try again:

sqlplus / as sysdba
shutdown immediate
startup mount
alter database noarchivelog;
alter database open;