Finding .one files on hard drive

This morning I tried to open onenote so I could start taking notes for class and the program didn't want to open.  It gave me an error message that, foolishly, in my haste, i didn't really pay attention to.  Something about a file possibly being corrupted.  It gave me 2 options (I don't remember what), I clicked one, and when the program opened all of my notebooks were there, but they were gray and empty.  They are not backed up on onedrive.  Onednote support was not able to recover them.  But they HAVE to be on my harddrive somewhere, otherwise I wouldn't have been able to close and open them all the time like I've been doing without losing data!  Does anyone know where they might be stored on the hard drive?  I cannot find them anywhere and they do not appear to be in my recycle bin.  

TIA