So, I bought this used M-Audio ProKeys 88 from some guy for $50, and when I first got it it played just fine. Only one problem: one of the keys was dead, and not just any, one in the center. So yesterday I took it apart, cleaned the contacts, put it back together... aaaaaaand no sound. Interestingly, the demo still works, but nothing happens when I press the keys. While I was working on it a jumper(?) fell out the pcb where the i/o was, but I managed to figure out where it came from and soldered a piece of wire in its place. Still, no sound. Really stumped on this one. There are two interchangeable ribbon cables; I have tried switching them around, but to no avail. Unfortunately, M-Audio has removed ProKeys entirely from their website, so no tech support. Also nothing really online that helps.