There are several possible reasons why midi control of sinfonia might be lost (such as a wrong button being hit), but performing a factory reset typically restores proper functionality. Try following these steps:

1. Just above middle C on the keyboard, there are 2 buttons labeled "+" and "-" Hold these buttons down while turning the keyboard off, and then back on (The power switch is on the back of the keyboard). You may let go of the + and - buttons only after the keyboard has been turned back on. Doing this restores the keyboard to factory settings. Picture: Oxygen 25 Reset

2. Then, simply reselect the keyboard in the Setup Wizard. You can find the option to run the setup wizard in the tools menu.