Cumulative sum of products

We have two different kind of orders: Order from Suppliers Order to Clients We need a query in which we show per week the stock available calculating the stock per week doing: Orders from suppliers - Order to Clients. We already made a query which is attached, but it doesn't show values when a week has no order. Data are in Greek so we have the translations in order to be easier to understand: Week >= Current_Week -> True false criteria Τρ.Εβδομάδα -> Running week GXCOMMERCENTRYKIND -> Type of order GXORIGIN -> Origing of order Ημερομηνία -> Date of order Αρ.Παραστατικού -> Number of order Παραστατικό κωδ. -> Order Code Παραστατικό περιγραφή -> Order Description Είδος περιγραφή -> Item description 1η ποσότητα -> Quantity of 1st unit measurement (pcs) 2η ποσότητα -> Quantity of 2nd unit measurement (Kg) Ημερομηνία Εξαγωγής -> Date of execution (Date that the stock will change) Εβδομάδα Εξαγωγής -> Week of execution (Week that the stock will change) Έτος Εξαγωγής -> Year of execution (Year the the stock will change) Συναλλασόμενος -> Client/supplier (trader) Σχόλιο 1 -> Comments of order Είδος κωδ ->Item code GXID -> Unique key of order Στοκ 1η ΜΜ -> Available stock in acumulative sum 1st measurement unit Στοκ 2η ΜΜ -> Available stock in acumulative sum 2nd measurement unit Ποικιλία -> Variety (Case result) Χώρα -> Country (Case result) Μέγεθος -> Size (Case result) Κλάση -> Type of product (Case result) In 1η ποσότητα ( Quantity of 1st unit measurement (pcs)) we already have a number with "-" when its from client that reduces the amount of products and a "+" sign when its from supplier. We have SQL SERVER 2008 R2