Does someone know a way to prevent a user from entering data into a cell
unless there is something first entered into different cell. Here is an
example of what I am trying to do.

=IF(A1="",disable data entry in D1,enable data entry in D1)
=IF(A1="",D1="")

The application is a time sheet. I want to prevent a person from entering
their hours until a billing code is first entered. In addition, if the
billing code is deleted then I want to delete the hours booked against it as
well.

Thanks for any tips

Best regards
GordL