ORA-12560 when 'connect / as sysdba' on 8.1.7

I have followed similiar threads, but have not seen an exact situation or solution, that I have not tried. I teach at a community college in central Florida. I access Oracle, numerous databases (SID's) through SQL*Plus, located on 2 Oracle servers (both servers are running Win2000). I can access any database, through the SYSTEM user, by way of:

1. My office PC, running WIN2000, with SQLNET.ora being used
2. On classrooms PC's, running Win98, with SQLNET.ora renamed SQLNET.bak (due to inability to connect to Oracle)
3. In alternate office PC, running Win2000, on another campus with SQLNET.ora being used

How the network is set up is a mystery. Access to the Novell servers for logging onto the classroom PC's are through one Novell server, access to the Novell server to logon on my office PC is a different server and access through the alternate office is another.

I CAN successfully connect / as sysdba on my office PC. However, after successfully logging onto Oracle through SQL*Plus (in classrooms or alternate office) Oracle responds with the following:

SQL> connect / as sysdba
ERROR:
ORA-12560:TNS:protocol adapter error

Warning: You are no longer connected to Oracle SQL> Thanks in advance. Received on Sat Feb 16 2002 - 12:39:14 CST