ORA-12560 TNS protocol adapter error

Question

I have installed both Oracle 12c and Oracle Client on Windows 8.1. The database was working fine until I installed Oracle Client Software alongwith Oracle Development tool for VS2013 as I wanted to develop a C# application that connected to Oracle database.However after I installed it I'm getting this error.
When I type the following sqlplus / as sysdba in cmd I get the following error:

ERROR
ORA-12560: TNS: protocol adapter error

I followed the steps on this link.

I Googled a lot and it seems that these are maybe interfering with each other. Can anybody help?

Answer 1

Most common issues:

• You just installed Oracle 12c database and you are yet to perform the mandatory post-installation steps.
• You want to connect remotely, but actually trying to connect to local instance, i.e. you are not mentioning the SID explicitly.
• The environment variables are not properly set.
• Last, but not the least, the database is not up.

As you have tagged Oracle 12c, I suggest you to first complete the mandatory post-installation steps. See Oracle 12c Post Installation Mandatory Steps.

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UPDATE Based on comments, OP has updated the question.

When I type the following sqlplus / as sysdba in cmd I get the following error:

You are connecting to the CDB and not to the PDB. As I have already mentioned here,

The most common misunderstanding is about “SQLPLUS / AS SYSDBA” usage.

Since we have checked the option to create database as a CDB, the “SQLPLUS / AS SYSDBA” command will always connect to the CDB.

So, you need to login as sysdba into PDB explicitly.

For example,

sqlplus SYS/password@PDBORCL AS SYSDBA

where pdborcl is the pluggable database.