weird thing with my mm 5700

[Serum]

i can't recall if it steers with the on/off switch on OFF...

It is possible (Like Brian says) that the controller is setup wrong. Set everything to neutral.

You did programmed it to your receiver/transmitter? here is the deal;

switch on transmitter, give a WOT, hook up the batteries (keeping WOT) switch on the speedo.. Wait till you hear the beeps, then go to full brake, wait for beeps again. Go to neutral, wait for beeps, and now the esc will give it's tipical mamba sound, telling you it's armed. If this all doesn't work, i suggest trying another receiver.