If power shuts off (display goes blank) then your battery is probably shutting down to protect cells from overdischarge, overcurrent, heat, etc.
If power does not shut off (display remains on) but motor stops responding to input, then the controller has shutdown becuase some limit has been exceeded.
If you have changed any settings in the display, try changing them back to what they were before. If you didn't note down what they were, you'd have to experiment with them one menu setting at a time, one value at a time, to find out if any of them affect your problem.
Otherwise, what specifically happened between the time the bike worked correctly, and the time it did not?