In a freshly installed version of Visio 2013, all of the UML shapes are missing. When creating a new diagram, I see various UML diagrams available under 'Software' including UML State Machine, UML Class, UML Use Case, UML Sequence, etc.
When I select any of those and click 'Create', a blank diagram comes up and where the shapes should be is a note that says "Where are the shapes? There are no stencils open. Click the More Shapes menu above to browse shape categories and open stencils."
I've searched through all of those options and cannot find any UML shapes. I'm guessing that there are other shapes also missing.