ORA-01033 with Oracle 12c

I have a freshly installed Oracle 12c instance (ORCL). While messing with listener.ora (trying to add a listener for PDBORCL) it happened that,

after I removed the section from listener.ora again, that my database is in error.

listener.ora:

# listener.ora Network Configuration File: C:\app\me\product\12.1.0\dbhome_1\network\admin\listener.ora
# Generated by Oracle configuration tools.

SID_LIST_LISTENER =
  (SID_LIST =
    (SID_DESC =
      (SID_NAME = CLRExtProc)
      (ORACLE_HOME = C:\app\me\product\12.1.0\dbhome_1)
      (PROGRAM = extproc)
      (ENVS = "EXTPROC_DLLS=ONLY:C:\app\me\product\12.1.0\dbhome_1\bin\oraclr12.dll")
    )
  )

LISTENER =
  (DESCRIPTION_LIST =
    (DESCRIPTION =
      (ADDRESS = (PROTOCOL = TCP)(HOST = Ora12c.company.de)(PORT = 1521))
      (ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC1521))
    )
  )