Your receiver's failsafe will kick in and either keep running at a certain rpm or shut down, whatever it is setup to do. Have you setup your throttle curves on the Tx? You may be running a set number across the board. Have your reprogrammed the ESC? I know when I received my used Trex 450 it was in flying condition with no battery, I still had to program the ESC. You may also need to reverse your throttle channel. If it is not reversed it will think you are at full throttle on start up, which should send you into ESC program mode.