The Yamaha-keyboard/synth is connected to the computer (iMac 27", middle of 2011, El Capitan) via USB (from the keyboard it's connected with two big cables, "in" and "out"), but won't work. Garageband says that a MIDI-device is found, but the keyboard can't be played on any tracks. Does anyone have some insight? It's a fairly old keyboard (it has a floppy disk!) so I'm worried it won't work as a MIDI-keyboard at all - does anyone know if some keyboards can be too old for MIDI-use, although they have MIDI-support? Are there any special settings that have to be made on the keyboard itself? I've googled this to death and have tried the most obvious things (restarting GB and computer, switching the cables, switching USB-slots, have tried all the different "audio in"-options in GB, have tried to use the sound/midi-settings app, installed some drivers from Yamaha etc), but nothing works. Gah. If anyone have any general tips or experience with the specific keyboard, Yamaha PSR-540, it is most appreciated! Thanks!