Need VBA code to use a data validation list

I have cell B9 which uses the Data Validation List function but before the user enters his selection in this cell, cell C8 must be populated with a value.

Ideally I want Cell B9 to display the list of names but only allow this selection to be entered if Cell C8 has a value in it, if no entry in Cell C8 then a warning message box pops up informing the user to enter their margin first.

Use data validation with a type of list and a formuls similar to

=IF($C$8<>"",$A$1:$A$9)