Can't connect to database after restarting, TNS Error

Question

I'm a little new to Oracle 10g administration. I successfully installed it on Oracle Enterprise Linux. Immediately after installation, I was able to connect to the default ORCL database using sqlplus. However, when I restarted the computer, I was no longer able to do so, even after restarting the listener service.
Here is the error I get:
ORA-12514: TNS:listener does not currently know of service requested in connect
descriptor
The other strange thing is, whenver I create a new database using dbca, immediately after that I can connect via sqlplus. However, if I perform a shutdown/startup, I get the same error as above. Restarting the listener doesn't make any difference.
A tnsping to my new database is successful but I can't connect to it from sqlplus.
Running the 'lsnrctl services' command immediately after making the new database shows it running but after a shutdown/restart only the default EXTPROC service shows.
Can anyone tell me why this happens and how to resolve it? Is there some other service I have to restart? Also, why does the listener not know of the service when it is explicitly configured in the tnsnames.ora file?
Note that I change my ORACLE_SID to the service name before attempting to connect.
Everything in the listener and tnsnames files was coded by the software, not by me.
Thanks for any help.
Here is my listener file:
SID_LIST_LISTENER =
(SID_LIST =
(SID_DESC =
(SID_NAME = PLSExtProc)
(ORACLE_HOME = /opt/oracle/product/10gR2)
(PROGRAM = extproc)
LISTENER =
(DESCRIPTION_LIST =
(DESCRIPTION =
     (ADDRESS = (PROTOCOL = TCP)(HOST = linux)(PORT = 1521))
(ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC1))
______________________________________________

Answer 1

I played around a little by deleting and creating databases. Here is my current tnsnames file:
TESTDATA =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = linux)(PORT = 1521))
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = TESTDATABASE)
ORCL =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = linux)(PORT = 1521))
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = orcl)
EXTPROC_CONNECTION_DATA =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC1))
(CONNECT_DATA =
(SID = PLSExtProc)
(PRESENTATION = RO)
I just made the database called TESTDATA. Here is the output of the command 'lsnrctl services', where the TESTDATABASE service refers to the database I just made:
[oracle@linux ~]$ lsnrctl services
LSNRCTL for Linux: Version 10.2.0.1.0 - Production on 11-JUL-2007 22:19:47
Copyright (c) 1991, 2005, Oracle. All rights reserved.
Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=linux)(PORT=1521)))
Services Summary...
Service "PLSExtProc" has 1 instance(s).
Instance "PLSExtProc", status UNKNOWN, has 1 handler(s) for this service...
Handler(s):
"DEDICATED" established:0 refused:0
LOCAL SERVER
Service "TESTDATABASE" has 1 instance(s).
Instance "TESTDATABASE", status READY, has 1 handler(s) for this service...
Handler(s):
"DEDICATED" established:13 refused:0 state:ready
LOCAL SERVER
Service "TESTDATABASEXDB" has 1 instance(s).
Instance "TESTDATABASE", status READY, has 1 handler(s) for this service...
Handler(s):
"D000" established:0 refused:0 current:0 max:972 state:ready
DISPATCHER <machine: linux, pid: 25175>
(ADDRESS=(PROTOCOL=tcp)(HOST=linux)(PORT=38662))
Service "TESTDATABASE_XPT" has 1 instance(s).
Instance "TESTDATABASE", status READY, has 1 handler(s) for this service...
Handler(s):
"DEDICATED" established:13 refused:0 state:ready
LOCAL SERVER
Service "test2.class" has 1 instance(s).
Instance "test2", status READY, has 1 handler(s) for this service...
Handler(s):
"DEDICATED" established:0 refused:0 state:ready
LOCAL SERVER
Service "test2_XPT.class" has 1 instance(s).
Instance "test2", status READY, has 1 handler(s) for this service...
Handler(s):
"DEDICATED" established:0 refused:0 state:ready
LOCAL SERVER
The command completed successfully
[oracle@linux ~]$
Now I'm connecting and here is my result:
[oracle@linux ~]$ sqlplus /nolog
SQL*Plus: Release 10.2.0.1.0 - Production on Wed Jul 11 22:21:24 2007
Copyright (c) 1982, 2005, Oracle. All rights reserved.
SQL> connect sys/pwd@testdata as sysdba
Connected.
SQL>
I am able to access the database from the OEM.
Now, here's what happens next. I shutdown the database from sqlplus and now when I restart, I get this message:
SQL> startup
ORA-24324: service handle not initialized
ORA-01041: internal error. hostdef extension doesn't exist
Now, if I exit sqlplus, enter again and try to connect, I get this error:
oracle@linux ~]$ sqlplus /nolog
SQL*Plus: Release 10.2.0.1.0 - Production on Wed Jul 11 22:28:01 2007
Copyright (c) 1982, 2005, Oracle. All rights reserved.
SQL> connect sys/pwd@testdata
ERROR:
ORA-12514: TNS:listener does not currently know of service requested in connect
descriptor
SQL>
Any solutions? I appreciate your help.