Double check the frequencies are correct on the transmitter and receiver, and that mute is not on. Then the next thing to check is that the pilot signal in switched on in the transmitter, if it is there will be a small P in the bottom left corner of the transmitter display. If not, go to the menu on the transmitter, then to advanced and press set, then go to pilot tone and press set, you can then change it to on by using the up down keys and pressing set.