It might be. Try changing up the servo connections to the reciever. ie. Change the throttle for the turret. See it if will start under the control of the turret stick. You will also be able to check your throttle stick, as it now will be lighting up the DBU LEDS

Did you check the three wire cable and ensure all connections are good. I had a wire break off one time and it was hard to see it was broken.

Your battery seems more then adequate, and if the above all checks out and the tank still won't start, try reheating the DBC solder poiints.