Welcome to the Board.
If I've understood you properly, when a checkbox is checked on one wb then you want a checkbox to be checked on another wb?
This will work - change the references etc to suit - based on a method provided by Aladin.
Private Sub CheckBox1_Click()
If [A5] = True Then Workbooks("Book1").Worksheets("sheet1").Range("B5").Value = True
Where A5 is the cell containing the first checkbox. (No doubt there is a shorter way to do this).
Does this help?