It was the modulator wheel! It is still a mystery as to why the tones weren't able to be changed since that wheel shouldn't affect being able to change tones, but regardless once I reset the wheel it's working great again so thanks!
My Casio previa is stuck on one tone ... doesn't change no matter what I enter. It did work great till now. How can I reset to factory spec? The directions say to hold down the plus and minus volume button while powering it up but that doesn't work. Hoping someone can help?