THANK YOU SO MUCH FOR YOUR HELP - I decided to avoid this problem for the moment, and use my old PC for the db, maybe I have to come back later on this, if it does not work any longer....
Thanks of the help of you all, I,'ve made some progress with my db, but now I have a big problem with conditional formatting
I want individual fields to show different coulours depending on conditons
my new PC works with win7.pro and Access 2013
on my older PCs (win.10 and win.xp) I was used to simply press the button of "conditional formatting" in the FormView and add the condition(s) for the colour(s) of this field - simple and enough for my purposes :-)
but this doesn't work any longer on my new PC win.7 pro: here I can see the Button (conditonal formatting), but it does not react at all...
thus I copied the DB to my older Pcs (win.10 and win.xp) and: there it works as usual - why not on win.7 ???
Guess it has something to do with the libraries (Modul-"Verweise"...) ????
where instead of Microsoft Accss 9.0 Object Library (as in win.10 and win.xp)
on my win.7 pro PC I dont have this Library
but now the Microsoft Access 15.0 Object Library....
(and in the selection list no chance to click the 9.0 library)
thus my questions would be:
1) how can I get back my Microsoft Access 9.0 Library on my Win.7 Pc ????
2.) any Idea if this could solve my problem ? and - if I do so - would this damage something else on my new PC???
and - what I also haven't found out yet - and my next question would then be: (to mark empty fields, which are dates)
3. how do I define a field-Value as empty if it is a date? ???? NULL doesn't work, " " doesn't work, <> doesn't work...