Make sure enough salt is used in the water solution (too much is fine)
Make sure the layers are correct. First, air cathode (black), then nonwoven fabric (white) and finally the magnesium sheet on top)
The cartridge may be pushed in too far or not far enough. Slowly push in or pull out until the wheels start spinning. In other words, gently ease the cartridge inward until you hit a sweet spot and the wheels begin to move. At this point you can let the cartridge go because there is no need to push it in any further.
When trying to get car to work, make sure your hand is not on back wheels keeping them from spinning.