If u want to connect client machine with the server then y are u going for listener. just make a service to connect to the main database. if u still need the listener try restarting the listener using lsnrctl in command prompt
The test you conduct on the server must use the Oracle Net stack, or it is not a valid test. This means, connect with a fully qualified user name, password, and service name such as sqlplus system/manager@dpl
If the above test is successful, then start testing the client. The same tnsnames.ora and sqlnet.ora you have on the server can be copied to the client. Then, test connecting from the client using the same fully qualified connection string: sqlplus system/manager@dpl
Keep in mind the ADDRESS lines in tnsnames.ora must point to your listeners, not your databases. All connection requests go to a listener, and the listener will then contact the database on your behalf to setup a shadow process for you (either by bequeath or direct hand off.)
In your example tnsnames, I recommend removing ADDRESS_LIST as it provides no value and changes the behavior of load balancing and failover which you want to trickle down from the DESCRIPTION block. Also, you really should replace the Oracle 7 "SID" syntax with the Oracle 8i and higher "SERVICE_NAME" syntax.