no the crystals can go in either way round and if it was the crystals you wouldnt get any life out of the tank.
Silly question but have you wired the the motors to the right place on the board?
Did you remove the wire coming from the on/off switch to the receiver board as this has been known to cause probs with the transistors.
iam having similar probs at the moment with 2 of my rx-13 boards and have now re-placed with the newer tk-rx14 boards Pm me if you want to know where i got them and i'll give you his e-mail addy
but first if it is the transistors they are relatively cheap and fairly easy to re-place just got to find out which one /all is gone
on the picture the red box shows where the transistors are undo the ally plate via the four screws and get them re-placed im no electronics genius but we have a few on here that might know where you can get re-placement ones from as im still waiting to hear about mine