Harvard style referencing

[Jennifer Brookes]

Hi,

I am having difficulty figuring out how to convert my references to 
alphabetical (Harvard style) in preparation of an article. I have been 
using lyx version 1.4.4, with document class article (REVTeX4), citation 
style natbib (Author-year) and  bibliography style agsm. When I compile 
however, no references appear and there are question marks where I would 
like the references to be. Before I was using natbib (numerical) and 
bibliography style apsrev, which worked fine, can anyone tell me the 
problem?

Many thanks
Jenny