Andy, the PCM flashes when the failsafes are transmitted, with a PCM system you need to turn on the transmitter, then the receiver and then wait for the PCM to flash. Until the reciever has received the failsafes it will default to last known position (very dangerous with a robot).

With 2.4GHz you should turn on the receiver before attempting to bind the transmitter.

First install your bind plug.
Turn on the receiver (light should be flashing).
Turn on the transmitter while holding the trainer switch to enter bind mode.
Wait until the light on the receiver goes solid.
Remove the bind plug.

The receiver will store the stick positions during binding as the pre-set positions for failsafing so make sure that when you switch the transmitter off the robot does not move (or creep). If it does you will need to redo the bind process with the sticks in the neutral positions.

Also to note, modelmatch will store seperate bind settings for each receiver. So if you change model on the transmitter, you will need to rebind the receiver.