No sound from Casio CTK-481

It USED to work. I had bought a MIDI to USB cable, and I plugged it in and it worked first try, but now it just won't work. GarageBand says that there is a MIDI input detected, but it won't make a sound like it used to. I don't think I changed the settings, but it's possible. Any clue as to what's going on? I also don't think that it's the MIDI cable. The lights are still on, and when I press the down arrow to the MIDI connection in MIDI Setup in the Utilities a yellow light blinks once every time I click it.