Oracle Database Discussions

Hi there!
I just installed Oracle database 10.1.0 on my home system. While the installation went fine, and the other configuration assistants also did their job, the problem started during the Database configuration assistant. After putting in and configuring all required details to make a database I clicked the 'Finish' button. At the instant the process of creation started a pop up appeared saying 'ORA-12546 TNS Permission Denied' asking me to ignore or abort.

I tried to start SQL *Plus with the username password - system/manager but it gave TNS protocol adapter error.

Can someone please advise me what to do? I have a Windows 7 32-bit PC named - Shikhar-PC. The contents of listener.ORA and tnsnames.ORA are as follows:

listener.ora*

SID_LIST_LISTENER =
(SID_LIST =
(SID_DESC =
(SID_NAME = PLSExtProc)
(ORACLE_HOME = D:\oracle\product\10.1.0\db_1)
(PROGRAM = extproc)
)
)

LISTENER =
(DESCRIPTION_LIST =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC))
)
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = Shikhar-PC)(PORT = 1521))
)
)
)

tnsnames.ora_


EXTPROC_CONNECTION_DATA =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC))
)
(CONNECT_DATA =
(SID = PLSExtProc)
(PRESENTATION = RO)
)
)

Any help would be appreciated! And by the way I am a newbie so please bear me!

Thanks.