thanks so much subdivision,btv and screwdriver, i finally solve the problem. after deleting the cokies,temporari files, the internte explorer did anice speed up in performance, but the problem of the vanishing download dialog still was there. i opted for make asystem restore and sent my computer back to the alst saturday, and after acouple minutes the lovely download window appears.
tahnk so much for your answer guys and suggestions.
i do use adaware it is a great tool and very necesary today.