The reservoir has 2 pumps. One for the windshield and the other for the headlights. I would suspect the pump but you say you can hear it running. You are going to have to pull a headlight and disconnect a hose to see where the problem is. Strange that both do not work. Peter is the shop foreman at my local dealer. This is what he has to say.
http://www.pca.org/tech/tech_qa_question.asp?id={F80A1D07-A8B6-4EE6-9147-A955B7A71E9D}
http://www.pca.org/tech/tech_qa_question.asp?id={F80A1D07-A8B6-4EE6-9147-A955B7A71E9D}
On preview the links don't work. Go to the PCA site under the tech section for Boxsters - electrical