Pancake requires at least .NET framework 4.5, which is shipped with Rhinoceros 6 but not with Rhino 5. Check the .NET framework downloader here.
Make sure you have .NET framework 4.5 installed
Check if you can find
Pancake category in component tab
If found, Pancake failed to load the menu. See Contact.
Check if all files belong to Pancake is unblocked. Unblock them if not. If it is a new installation, you should at least make sure
Pancake.gha is unblocked, as it will notify you if other components have any trouble.
If problem persists, see Contact.