woo commerce error: quantity selection not showing

kindly help me urgently,
though i never got a reply here but i am tryng to find a solution fast if you can than plz help me
i am using woo commerce plugin suddenly the quantity selection in the product page got removed and now am not able to apply that again.
as well as single unit of each product is allowed to ad to cart not more than that kindly help me out urgently!! how can i solve this issue