I agree with Scale, it sounds like the throttle was reversed which could have put the ESC into program mode. If that has happened you will need to reverse the throttle channel and reprogram back to the settings you want. The ESC instructions should be enough to get you through the programming using throttle stick positions at specific tones from the motor. It's a bit of a pain in the butt. It would be much easier to obtain a program card if one is available. Either way, the instructions that came with the ESC will be a good place to start.