Open windows explorer and browse to My Documents -> Electronic Arts -> The Sims 4 -> Saves. Please post a screen capture or the text list of files which are in this directory. If you don't see this directory or you've found that it's empty, you can try searching your entire computer for any file containing Slot_ or .save
If more than one person uses your computer, be sure that you're logged in with the windows user account which was originally used to install the sims and create your neighborhoods. If you've changed windows accounts, your save files might be under the documents directory for the other profile - this is unlikely if you don't login to windows with a password and don't share your computer.
If you locate those files at another location, it is possible to restore them even after you've started a new file.