Have you emailed them recently? Have you copied any onto usb? Have you
edited them on a different computer recently?
Any of those sorts of things mean you have some sort of informal back-up
that may help you recover.
What happened just before losing spreadsheets? Is it just MS Excel that
can't find them? Also if you can, please let us know what Operating System
(Win 10, Xp, Ubuntu, OSX, etc) or even just what platform (ie Windows, Mac,