Hello, Desperately need help. Phones don't ring at desks (caller hears tone in earpiece indicating ring).

Called King industries. They said sometimes is result of relay failure in machine, and to move incoming lines over one slot in order to use a good relay. Machines allows for four incoming lines. We only use two. Moved incoming line on #3 to #4. Tried all combinations, phones still do not ring.
Can anyone help?

This is second machine. First was replace by warranty for same problem. This is not good.