You got it from this company: CNC Routers | Industrial CNC Routers | Afforadable CNC Routers | Intergrated CNC Routers | Router Systems ? They say they provide free tech support if you bought it new from them - did you ask them about this issue? If so, what did they say? If it doesn't work, can you send it back? They seem to be in the USA someplace, although they don't say where...
But no, if it doesn't communicate, switching out the motors won't help. It sounds like it's doing something when you give it a command, just not what you want it to. Have you tried Motor Tuning in Mach3?