changed tns names file and cannot connect and view the datafiles space

I am an dba and I changd the tnsnames file and then back and I am unable to connect to oracle using toad (but I can with sqldeveloper, using the same tnsname file) so is there some other setting in toad that I a missing

A little more information would be helpful. Does the dropdown on the login screen still contain the entries of your tnsnames.ora file? What happens when you try to connect?