FINDING "FILE MANAGER"

I can't find File Manager on my site. It was there, once upon a time - but now it's gone! When I bring a page up to edit, and I'm asked if I want to start from the last save or not, it doesn't make any difference which option I choose, I still can't get the File Manager.

I have the new Microsoft operating system (8 ?). Could this have anything to do with it?