If you have an ohmmeter; test the midrange speaker(disconnected) for continuity. If you have no reading: either the lead-in wires have broken, or the voicecoil has opened up. If you have no ohmmeter; use a 1 1/2 volt battery(like a AA cell) and a couple wires to see if the cone moves when you energize the midrange. Just flick the wires across the midrange speaker's terminals. If the midrange is good; the trouble is in the crossover or wiring. Components can open up without apparent/obvious damage.