Measure the voltage of the LiPo pack either with an external meter or with the charger and make sure the pack is charged...voltage above 11.5 volts.  If so then the speed control ESC is not providing 4.8 or 6.0 volts to the receiver  provided the ESC has a built in BEC (battery eliminator circuit). If not then it must have an external BEC to provide regulated voltage to the receiver.
Did this set-up ever work for you? If so then I'd suspect the ESC and /or the connections. If the ESC has a built-in BEC the it sends voltage down the red lead of the throttle plug to the receiver.