Grants solution is probably right... but Id expect some clicking and humming if you have jammed the gearboxes and effectively stalled the motors.

try running leads direct from the battery to the motor terminals to see if it moves...

When you say you are getting voltage to the motors, have you measured it? try sticking a small lightbulb across the terminals where the motor would normally be, it should get brighter as you apply power.. or use a volt meter if you have one.

have you checked the reciever battery?
connect up a servo to a spare channel and see if it moves?

also worth checking simple things like you have the same crystal in the Rx` and Tx... and that the Rx crystal hasnt fallen out...

Are the main batteries both charged fully.. if you have a duff cell in one pack it can stop everything when you put a load on, but it may register a full charge on a voltmeter.(its happened to me and drove me round the bend trying to find out what the problem was)

equally if the main batteries arent fully charged , some speedos wont have enough ooomph to open the relays (though i think electronize operate down to 6v)