Macro does not run based on cell value

[Bigmal70]

I am on the committee of my local youth football league and I am trying to put together a simple to use Excel 2003 spreadsheet for committee members to issue fines to clubs.

I have created the attached file which allows them to enter the required data in the yellow cells and then generate an e-mail by clicking on the 'Send E-mail' button.

What I would like to do is not run the 'Send E-mail' macro if the data is incomplete but instead displays the message 'Data is incomplete. Please check and try again'. If the data is imcomplete the value in cell D13>0.

Can anyone help?