Oracle multiple databases only able to access one database
Database Windows Service Status &quot;Running&quot; does not necessarily mean the database is open and available. The database can be in all states &quot;down|nomount|mount|open&quot; while the Windows Service says &quot;Running&quot;.
- C:\&gt;lsnrctl status # will tell if the database service has been exposed/made available.

You should validate the state of each database by:
set ORACLE_SID=&lt;SID&gt;
sqlplus / as sysdba (OS auth. Make sure your user is member of local group ORA_DBA)
SQL&gt;select * from v$instance;

Check the alert_.log for errors. You will find the alert log in your Oracle Software trace folder.
Best of luck.