Where's my Network Alias list in Oracle?
tnsnames.ora should be located in TNS_ADMIN, which is defined as ORACLE_HOME/network/admin/.

Go to a command prompt (assuming Windows from your mention of "c:\") and execute the following:

echo %TNS_ADMIN%

echo %ORACLE_HOME%


Verify the directories returned, make sure that your tnsnames.ora file is in there.