ORA-12514: TNS:listener does not currently know of service requested in connect descriptor

ORA-12514: TNS:listener does not currently know of service requested in connect descriptor is the most common and most frustrating error in Oracle

What it means is, In tnsnams.ora, the service_name parameter is in correct or not available

TNS_Service =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = machine_name)(PORT = 1521))
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = Database_Name)
)
)

In my instance, I have Oracle hosted on a Windows box, and my OracleServiceDatabase_Name
was not started.

Once I started the Windows service , I was able to connect to the database

Start->Run->Services.msc

Locate the OracleServiceDatabase_Name, and right click and start the service.