Incoming chat can be disabled in three ways: 1) audience is enabled, in which case you should be seeing double text from the controller (disable "chat hook" in the cortex menu); 2) the audio subsystem is disabled or restricted some how—could be extremely long radiation but more likely a mangled power profile (try "@reset bonds" and then toggle "audio" in the "subsystems" menu); or 3) a wayward RLV restriction from the relay (in which case the RLVa "Restrictions" window will show the source as a (child) prim of the controller)—at a minimum this will go away if you relog or re-attach the controller.