You haven't given us a lot of info to go on.
Have you tried setting the endpoints?
To do this:
REMOVE YOUR PROP (for safety)
Turn on your radio, throttle trim all the way down (leave it there), move the throttle stick to full throttle, plug the battery into the ESC. The motor should NOT spin, the ESC will beep beep (high endpoint learned), move the throttle stick to off, (the low endpoint is now learned). The ESC should now arm normally and be ready to use.