Sometimes when I'm driving my MT, it will stop cold for no reason at all. The battery is usually charged and all ESC lights are on. The radio batteries are fine as well. However, when I go in reverse and go forward again, it will respond fine.
Now all you need to do is try another motor......Make sure that all your pins on the tab that go into the rx are all in......sometimes if ones keep changing there setup around the little pins dont go all the way in causing a weak connection.