It sounds like either the User account or the User Documents folder was moved, possibly manually by dragging it (even accidentally) to the desktop. This is hard to put back to default but I'll give you the best tutorials on the web for it, and also alternative options:
Follow the steps here to restore the User account's Documents (and any other missing User folders) to the default location: User Folders - Restore Default Location
But if the User account itself is no longer in place then you may need to restore it following the steps contained in this tutorial to reverse it: User Profile - Change Default Location
This is a complicated operation that may best be abandoned to eitherCreate a NewUser Account for the install or do a Clean Reinstall Windows 7
If the Documents folder was moved to a Network drive, then it's possible (though unusual) that the files may have been moved to that location on the network. But this would almost have to be done deliberately since moving the User folders requires agreeing (or not) to move all the files in them to the new location.
The best way to try to find the files if they're still on the PC is to type keywords from Documents into the Start Search box to see if they're found. Be sure to also check under the User account to see if it's still there but no longer an official Shell User folder (signified by the document insignia in the corner).
Feel free to ask back any questions and let us know how it goes.