Oracle Database Discussions

hi everybody. i can connect my localhost via sqlplus.

C:\sqplus <enter>
username
password
okey
..
..
SQL>...

i can connect, there is no problem.
But, if i want to connect except sqlplus for example with plsql developer, i cant connect the database.( also i cant connect with jdbc )
Firstly, i was getting the ora-12545 error:
"ORA-12545: Connect failed because target host or object does not ..."

then, i am trying the edit tnsnames.ora and listener.ora, i changed the host as a 127.0.0.1 .

so, again i am trying the connect to the server with plsql developer, this time i am encountering this error :
"ORA-12514 : Tns: listener does not currently know of service requested in connect descriptor."

how can i solve this problem? as i said top of the page, i can connect with sqlplus.
thanx