That my friend sounds like one of two things: a faulty motherboard (most likely) or a short. When the tank turns off due to low voltage the headlights will blink still and you can restart the tank, though it wont move (the battery will cut off the tank again). However if you try to shoot and it completely shuts down then most likely it is a faulty motherboard. The easiest way to tell is to hook one thing up at a time and test the board and see what works such as:
- Start the tank with just the sound card, speaker, and main power cable installed.
- If the tank starts and goes through the motions then there is a good possibility there is a short somewhere. You can figure this out by turning the tank completely off and plugging one thing in at a time and starting the tank between to see if the functions have stopped.
- Try only plugging in one of the motors at a time and swap from the left to the right side motor outputs on the board to see if you might have a motor that has failed.
The TG boards are usually pretty darn reliable and safe. If the first one failed after operation (as in you drove it a bit before it failed) then installing a second one without checking for the initial failure reason might have also caused this one to fail too. However generally they are pretty solid. Do you have a video of this so we can see a bit better to help?