This is my tnsnames.ora. "PRDB" is my database name and "desktop" is machine/host name. You can cut and paste this tnsnames.ora into

ORACLE_HOME/network/admin or ORACLE_HOME/net80/admin whichever is relevant for your installation and edit database name and machine/host name. It shoud work. If not try posting errors.

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# TNSNAMES.ORA Network Configuration File: D:\D01\Ora8i\network\admin\tnsnames.ora
# Generated by Oracle configuration tools.

PRDB =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = desktop)(PORT = 1521))
)
(CONNECT_DATA =
(SERVICE_NAME = prdb)
)
)
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