ORA-12528 All appropriate instance are blocking new connections

C:Documents and SettingsAdministrator>sqlplus
C:Documents and SettingsAdministrator>set oracle_sid=dbiwm

C:Documents and SettingsAdministrator>sqlplus

SQL*Plus: Release 10.1.0.4.2 – Production on Thu Jul 8 15:38:26 2010

Copyright (c) 1982, 2005, Oracle. All rights reserved.

Enter user-name: sys as sysdba
Enter password:

Connected to:
Oracle Database 10g Enterprise Edition Release 10.1.0.2.0 – Production
With the Partitioning, OLAP and Data Mining options

SQL> shutdown immediate
ORA-01507: database not mounted
ORACLE instance shut down.
SQL> startup mount
ORACLE instance started.

Total System Global Area 1048576000 bytes
Fixed Size 792200 bytes
Variable Size 1012132216 bytes
Database Buffers 33554432 bytes
Redo Buffers 2097152 bytes
Database mounted.

SQL> shutdown

ORA-01109: database not open
Database dismounted.
ORACLE instance shut down.
SQL> startup
ORACLE instance started.

Total System Global Area 1048576000 bytes
Fixed Size 792200 bytes
Variable Size 1012132216 bytes
Database Buffers 33554432 bytes
Redo Buffers 2097152 bytes
Database mounted.
Database opened.
SQL> conn wh/wiwm1974@oracle-server
Connected.
SQL>