ORA - 12154 TNS: Could not resolve service name DBA Studio

I downloaded Personal Oracle 8.1.7 and extracted it to c drive on this windows 2000 pantium 4. I used the Database configuration Assistant to set up a database. I have checked my listener.ora and sqlnet.ora as well as tnsnames.ora - all seems fine. When I go into DBA Studio I cannot coonect to my database without having the TNS error.

I can connect system/manager in sqlplus ok.

pinged my machine ok.
net start showed me that listnere is running.

When I run tnsping service_name I get TNS - 03505 Failed to resolve service_name.

I have substituted the host with the actual ip address - no difference.

What is going on ??????

Help!!!!!!!!