If you have checked the suggestions in the previous answers, then it is certainly possible (but probably not that easy) to empty the folder where the Shapes are stored. If that has happened, then reinstalling Photoshop would fix it.
Just for clarity, are you looking in the library or in the Custom Shapes drop down?
For the library - it will store shapes that you put there. Shapes are stored under "Graphics". Example below of a shape captured and transferred from Adobe Capture:
For the custom shape tool, first you need the custom shape tool selected
then from the options bar click as shown. If 1-3 do not work, click on Reset Shapes.
If you still don't get any try a Preference reset (Preferences - General - Reset Preferences on Quit). If that still does not work, try an uninstall and re-install (which is a fairly quick operation from the CC desktop app).