I just got Moho Pro 14. It came with a bunch of styles and I was using them a while with a few different files.
Now I opened one of the files I was working on and the styles are no longer there.
The default styles are loaded from a file when you create a new project file. After these styles are loaded, they can be edited and removed like any style, so maybe you accidentally chose Delete Unused styles and removed them from the project.
You can bring the default styles back into the project by selecting File>Import>Moho Styles... and loading this file:
If you need to do this often, you can copy this file to a more easily accessible location. Optionally, you can add a project containing the Styles to the Styles area in the Library window and then drag them into your active project.