Out of control - only goes full speed backwards!

I've bought a zoomer dino on Ebay, but I think its faulty. I cannot control his movements - he moves a few times and then goes full speed backwards. It doesn't stop, inevitavly bumps into something and then keeps on spinning his wheels (while upside down) on max speed. I also have problems getting it into gesture mode. I tried pushing the button on his back but without success. My son loves his dino, but it's no fun with it being completely out of control and racing backwards all the time. Any help appreciated!