check cells

Hi

You can use a custom validation to range P15:Q18 for not allowing the users to use this range unless if the other range is full of data using this formula in custom validation bar

Formula:

=COUNTA(N4:O11)=16

but you can not force the users to don't delete data without to use VBA.

edit: because as i understand you need to allow them to type anuthing in first range but you don't want to allow them to delete data in that range.