I had to reinstall Win 10, so I saved my original APPDATA eM Client folder to use with the new eM Client install. New install does not display any of my old emails, contacts, or calendar entries.
The location of the folder is very specific. If you placed it in a different location, open eM Client and go to Menu > Tools > Settings > General > Storage. Click on the icon and find the location of the copied database. Restart eM Client.