VexRC Transmitter and Receiver

The robot uses the Vexplorer transmitter and receiver (the only thing the school had) and two-wire motors. It has worked before and nothing has changed since it has stopped working.

The RC system has stopped working for no apparent reason. The transmitter and receiver both turn on, and the motors can be run by manually hooking them up to a battery or putting them into one of AUX ports, however, I cannot control the motors from the remote, which just doesn’t do anything. I have checked all of the batteries, connections, and circuits, all of the usual suspects, and cannot find a problem there. Is there a way to determine if there is a problem with the radio system? Or to just override the radio system completely and wire the remote directly to the receiver in order to avoid building my own controller? Any help would be appreciated.