ORA-03114:	not connected to ORACLE
Cause:	A call to Oracle was attempted when no connection was established. Usually this happens because a user-written program has not logged on. It may happen if communication trouble causes a disconnection. In addition, this message could occur when ALTER SYSTEM KILL SESSION or ALTER SYSTEM DISCONNECT SESSION were issued with the IMMEDIATE qualifier because, in those cases, the client's connection to the database is terminated without waiting for the client to issue a request.
Action:	Try again. If the message recurs and the program is user written, check the program.

1)In the simplest of terms, the Oracle*Net architecture is like peeling on onion, with one transport layers nested inside the inner payer. The lowest level of Oracle transport is TCP/IP (or rarely other protocols), where the packets are shipped between the servers.
To troubleshoot & diagnose Oracle connectivity problems, I like to start at the simplest, outermost level, and follow this checklist:
1. Check with "ping" using the IP address ("ping 198.11.34.43"
2. Check with "ping" using DNS name (e.g. "tnsping uranus")
3. Check with "tnsping" using TNS service name
4. Sign-on to SQL*Plus with a remote user ("connect fred/flintstome@remote_link"
5. Within SQL*Plus, try a select from table@remote_db_link
2) Or you can check more
1. Verify there is no firewall, router setting which terminates connections which are active for longer than x minutes.

2. Verify there is no firewall, router setting which terminates connections which are idle for longer than x minutes.

3. Use latest version of the Connect wire protocol driver for ODBC for Oracle (some issues were reported with early versions of 4.0 and 4.1 with relationship to Oracle sending a probe packet).

4. Verify Oracle configuration. Let the database send a packet every x minutes, so that the firewall, router,... does not close the connection due to being 'idle'.

Can you establish a connection using SQL*Plus ?   Check that first.