Did you charge the batteries fully? And do you have everything hooked up as per the instructions? Many speed controls will kick off if the battery voltage is too low.

Do you have end point adjustment or anything like that on the throttle stick on your TX? It's possible to have the EPA on a TX set so that you can't get the throttle low enough for the speed control to think it's in the full down position. Try full down throttle and full down trim.

Beyond that, check the wireing carefully for loose connectors or a bad connector job.

If none of that works, seek out someone in person to take a look at it. Or maybe try in the electrics forum here or on ezone/rcgroups. They have a lot of real electric experts over there. I just dabble with them.