Hide rows based on cell content

Ok Gary
I'm closer to understanding "pop up" vs "Drop Down" and you are using a validation cell.

The answer is that you need someting to trigger your code. I'm assuming the code above is located in a Module and not behind the worksheet.

You need to create an event that calls the code in your module. You do this with event code that is located behind the worksheet.

Read http://www.cpearson.com/excel/Events.aspx and then
http://www.ozgrid.com/VBA/vba-intersect.htm

Or look at my attached example that creates an event behind the worksheet that calls your code.
If I was doing it for real I'd test the cell C13 using Target and call the code only if it was what changed.