I'm guessing that there is probably an issue with the configuration of your listener. First you can check the status, stop, and start the listener service using the following:
status:
lsnrctl status
stop:
lsnrctl stop
start:
lsnrctl start
If that doesn't work it may be a configuration issue with the listener.ora file itself. The default listener.ora file should look like this:
LISTENER =
(DESCRIPTION_LIST =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC1))
(ADDRESS = (PROTOCOL = TCP)(HOST = hostname)(PORT = port_number))
)
)
SID_LIST_LISTENER =
(SID_LIST =
(SID_DESC =
(SID_NAME = PLSExtProc)
(ORACLE_HOME = oracle_product_home_directory)
(PROGRAM = extproc)
)
)
Hope this helps.
-V