An update:

I created a new workbook and tried my worksheet_calculation event and
it seems like the broblem in not this event.
The problem is the validation list.
If I open the the file and close it (when no validation list is
selected or clicked in) the file closes as usual. but if the selected
cell is a validation (last saved like that) or if I click in any
validation list (without changing or even opening the list) it asks me
if I want to save changes. If I click Yes it saves the file and asks
again. It goes on and on till I choose No.
It doesn't even give me a chance to click in anohter cell. what can I
do? What I have done wrong that it creates this problem?