Hi open it up look for any lose wires on the battery box and make sure all plugs are pluged in give em all a push down.
also look at the board with the crystal see if any wires are lose and also try pulling the crystals out of the tank and radio and putting them back and trying it again.

Another thing try bending the tabs in the battery box with a small screw driver first even before taking it apart... sometimes the AA's nipple top don't reach all the way and contact the metal part in the tanks...I put a tiny svrew driver behind them all and gently pry back so the metal section bends out away from the chassis a little so it will contact the batteries better.

Hope this helps.