Here is the schematic for the Aquarium car.
The first item to check is that all wiring is intact from the rollers.
The next item to check is the on/off switch. Jump the switch out and see if the car works. Next in line is the 10 ohm, 2 watt resistor connected to the red wires. If that checks OK, chances are the circuit board is history.
The parts layout and numbers is here.
Larry