SQL Developer cannot connect to Oracle database, yet sqlplus can! I am having a problem connecting sql developer to my Oracle 10g database.  sqlplus is able to connect fine, but when I try to open the connection in sql developer, I get 'ORA-12514 TNS does not know of service' error.  I have tried modifying my tnsnames.ora file.  It has the following:

COTT3 = 
 (DESCRIPTION =
  (ADDRESS = (PROTOCOL = TCP)(HOST = localhost)(PORT = 1521))
  (CONNECT_DATA = 
   (SERVER = DEDICATED)
   (SERVER_NAME = COTT3)
  )
)


Can anyone assist with any other files I may need to modify or let me know where im going wrong?

Thanks

UPDATE
Output of lsnrctl status

 [oracle@VM-COT-DEV1 ~]$ lsnrctl status

LSNRCTL for Linux: Version 10.2.0.1.0 - Production on 02-FEB-2012 13:57:20

Copyright (c) 1991, 2005, Oracle.  All rights reserved.

Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=localhost)(PORT=1521)))
STATUS of the LISTENER
------------------------
Alias                     LISTENER
Version                   TNSLSNR for Linux: Version 10.2.0.1.0 - Production
Start Date                02-FEB-2012 13:01:25
Uptime                    0 days 0 hr. 55 min. 54 sec
Trace Level               off
Security                  ON: Local OS Authentication
SNMP                      OFF
Listener Parameter File   /opt/oracle/oracle/product/10.2.0/db_1/network/admin/listener.ora
Listener Log File         /opt/oracle/oracle/product/10.2.0/db_1/network/log/listener.log
Listening Endpoints Summary...
  (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=127.0.0.1)(PORT=1521)))
Services Summary...
Service "PLSExtProc" has 1 instance(s).
  Instance "PLSExtProc", status UNKNOWN, has 1 handler(s) for this service...
The command completed successfully

enter code here
Try this:

COTT3 = 
 (DESCRIPTION =
  (ADDRESS = (PROTOCOL = TCP)(HOST = localhost)(PORT = 1521))
  (CONNECT_DATA = 
   (SERVER = DEDICATED)
   (SERVICE_NAME = COTT3)
  )
)


If that doesn't work, replace "SERVICE_NAME" with "SID".

Put this in $ORACLE_HOME/network/admin/listener.ora:

LISTENER =
  (DESCRIPTION_LIST =
    (DESCRIPTION =
      (ADDRESS_LIST =
        (ADDRESS = (PROTOCOL = TCP)(HOST = localhost)(PORT = 1521))
      )
    )
  )

SID_LIST_LISTENER =
(SID_LIST =
    (SID_DESC =
      (SID_NAME = COTT3)
          (ORACLE_HOME = /opt/oracle/oracle/product/10.2.0/db_1 )
    )
  )


Then restart the listener with:

lsnrctl reload


Are you 100% sure that the database has started up?

Does:

ps auxww | grep pmon | grep -i cott3


... produce any output?