------可能你的实例不是自动启动的，你启动的只是数据库服务
C:\Documents and Settings\nervermore>sqlplus /nolog

SQL*Plus: Release 10.2.0.1.0 - Production on 星期二 12月 21 17:02:33 2010

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

SQL> conn / as sysdba
已连接到空闲例程。
SQL> startup
ORACLE 例程已经启动。

Total System Global Area  192937984 bytes
Fixed Size                  1248044 bytes
Variable Size             138413268 bytes
Database Buffers           50331648 bytes
Redo Buffers                2945024 bytes
数据库装载完毕。

------解决方案--------------------
探讨


实例是自动启动的。后来改成手动启动，启动出错了。新建了一个实例，建好后可以用，重启电脑后又不行了。真是费解。跟系统或者网络有关系吗？


------解决方案--------------------
还有一种情况是  要把listener.ora 内容 修改成如下：

# listener.ora Network Configuration File: E:\oracle\product\10.2.0\db_2\network\admin\listener.ora
# Generated by Oracle configuration tools.

SID_LIST_LISTENER =
 (SID_LIST =
   (SID_DESC =
     (SID_NAME = PLSExtProc)
     (ORACLE_HOME = E:\oracle\product\10.2.0\db_2)
     (PROGRAM = extproc)
   )
   (SID_DESC =
     (GLOBAL_DBNAME = ORCL)
     (ORACLE_HOME = E:\oracle\product\10.2.0\db_2)
     (SID_NAME = ORCL)
   )
 )

LISTENER =
 (DESCRIPTION_LIST =
   (DESCRIPTION =
     (ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC1))
     (ADDRESS = (PROTOCOL = TCP)(HOST = 127.0.0.1)(PORT = 1521))
   )
 )