ORA-12528: TNS:listener: all appropriate instances are blocking new connections 
Cause: All instances supporting the service requested by the 
       client reported that they were blocking the new 
       connections. This condition may be temporary, such as at 
       instance startup.
Action: Attempt the connection again. If error persists, then
        contact the administrator to check the status of the instances.

select status from v$instance;

select logins from v$instance