[Zip Zap Pro]

My friend and I tore apart his ZCar to look at the innards. We don't think we tore anything but we changed the motor, gear, and back tires. They are all Zip Zap pieces...oh, and we tore the LED out. Anyway, then we tried driving...and wouldn't budge. We changed everything back to normal then checked the inside to make sure nothing was missing but it was all the same. Then it still won't move! So we decided to look inside the controller to see if we fried anything....nope....everything is a-okay but won't move. I don't care if it doesn't work anymore, I just want to know whats wrong!