Blank fields on form load

Hi there,
I have a form which has 2 text boxes, a combo box and a sub form in it
(which reads from a query. The query reads from the table).
On load, I would like the fields in the text boxes and combo box to be
become blank. If I use the "" or 'null' instruction then this in turn
makes the corresponding field in the sub form blank which in turn makes
the query field blank and the table field blank!
If I then change the combo box option, this is then inputted in the
field in the query that was left blank on the form load, therefore
making the data incorrect.
How can I stop it doing this because, if this happens, it does not
search the database correctly and I am left with false data in my
query?
Any help is greatly appreciated!
Many Thanks.