There is one common problen that causes this. Infront of the rear wheels there are two housings for the indepentent hydrostatic transmissions. There is one gold colored shaft with a ninety degree angle on it sticking out from EACH of the housings on the top front. Again these are on both sides and they each need to be pushed downward so that the rods can then be pushed backward into the transmissions to inguage them so both of the wheels are powered.