How to fix ORA-01502: index or partition of such index is in usable state?

I am so desparate of getting the following issue resolved soon: (p.s. I have posted the same issue in the Oracle Forms community & sorry for the duplicate.)  

I received the “ORA-01502: index or partition of such index is in un-usable state” error from one of our Oracle forms, and the problem was caused by using SQL Loader w/ the "DIRECT" load option in our production database.  As a result of that, the system won't allow me to insert or delete rows from the problematic table.

When I tried to delete the duplicate rows from the table, I received the "ORA-01502: index or partition of such index is in un-usable state" error message;