(急)oracle 连接问题

弄了两天了,ORACLE连接老是出问题,请高手帮忙:
我用的是ORACLE 10G 在ORACLE SQL*PLUS中输入用户名 口令和主机字符串后都是提示:
ORA-12514:TNS:监听程序当前无法识别连接描述符中请求的服务.

而在PL/SQL 中,输入用户名与密码,选择数据库,总是出现未响应这种情况.
如果把CONNECT AS 选择SYSDBA又能连起.不知道是怎么回事:
listener.ora文件:
# listener.ora Network Configuration File: D:\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 = D:\oracle\product\10.2.0\db_2)
      (PROGRAM = extproc)
    )
    (SID_DESC =
      (GLOBAL_DBNAME = myoracle.172.16.32.45)
      (ORACLE_HOME = D:\oracle\product\10.2.0\db_2)
      (SID_NAME = myoracle)
    )
  )

LISTENER =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = 172.16.32.45)(PORT = 1521))
  )
tnsnames.ora文件:
# tnsnames.ora Network Configuration File: D:\oracle\product\10.2.0\db_2\NETWORK\ADMIN\tnsnames.ora
# Generated by Oracle configuration tools.

MYORACLE =
  (DESCRIPTION =
    (ADDRESS_LIST =
      (ADDRESS = (PROTOCOL = TCP)(HOST = 172.16.32.45)(PORT = 1521))
    )
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = myoracle.172.16.32.45)
    )
  )


希望高手能帮我解决问题