problem with new system.

ok, my friend and i just spent 8 days setting up a very nice sounding system in my car but i've run into a small problem. I've got 4 MB Quart Premium line PKC 116s (60 RMS 130 max) powered by an alpine V12 mrv-f307, a 10" Orion XTR10 (250 RMs 500 max) powered by an alpine v12 mrv-t407, a kenwood excelon kdc-x815 head unit and a kenwood kdc-c662 6 disc changer. everything was running great for a few weeks until the changer stopped working. i checked the cables and everything, and i can still take the cartridges in and out, but the head unit doesn't pick it up at all. could it be a bad cable? what do you think could be the problem?

this is in an 89 civic hatch, if that helps any. everything besides sound is stock.