VEXPlorer Mystery! Need your help to solve!

I have a VEXplorer set used with with Vex (Blue) Transmitter and Receiver and standard two-wire motors. This setup was working perfectly and then abruptly stopped (no dropping anything, mishandling, etc). The transmitter and receiver both turn on (fresh batteries), and the motors all work (can be run by manually hooking them up to one of AUX ports). The motors will not operate with input from the transmitter on any of the channels. All of the batteries, connections, etc have been checked and cannot find a problem. We have also taken the robot outside away from any signals in the house that might be interfering. The transmitter and receivers currently in use are actually brand new. They were purchased to replace the original set that did the exact same thing a couple of weeks ago. Anyone have any ideas how to solve the mystery of the disappearing radio frequency (27MHz) on the VEXplorer set?

I can not really help you troubleshoot, but offer you what I did when the same thing happened. Go to vexrobotics and buy a signal splitter, then check ebay for the old style crystal radio. Schools also have those old remotes piled up with no use for them.
Then the only thing you would need would be a matching pair of crystals which you can get pretty cheap usually. I tore the vex blue remote and splitter all the way down and could not fix it. Vexplorer is a cool little robot.