Is the ZZ knob/dial moving, but the needle isn't? Or is the knob/dial stuck? Have you opened up the top? There may be a spring broken/disconnected which moves the needle back to center (or L or R) when not in ZZ. If the knob/dial doesn't move then I would start oiling everything that even looks as though it moves up top, including in the nose end where the needlebar moves left and right, and then wait and try again.
I am not familiar with this machine, just taking some guesses based on other machines.