Divide and conquer....do not mean to insult your intelligence, but....is everything plugged in ?  don't look, get down and check.  /cords can go bad, get a continuity checker and make sure ALL your cords are good.  CAn you just play athe keyboard by itself ?  Then its good.  CAn yu just play MM by itself ? then its good.  Have yu pushed a Mute button somewhere ?  Aare you using headphones or a speaker system ?  Is a Volume contarol turned off or down ?  CAn you bypass athe Turtle Beach product to get music  ?  Make up a check list so you don't overlook something or repeat a process over and over.  Where were yu and what were you doing the LAST time everything worked ? and then what did you do next ?....maybe thats whats wrong...un-do waht yu did last.  Don't  be in a hurry, otherwise you might overlook.

Hope some of this helps. Good luck