Listener Status Blocked
A NOMOUNT instance stays in BLOCKED status with dynamic registration. You need to use static registration to connect a NOMOUNT instance remotely.

Add the below to listener.ora and restart the listener:

SID_LIST_LISTENER=
(SID_LIST=
 (SID_DESC=
  (GLOBAL_DBNAME=ORCL)
  (SID_NAME=ORCL)
  (ORACLE_HOME=/u01/app/oracle/product/12.1.0/dbhome_1)
 )
)


Of course, change the values of variables accordingly to your environment.