This fix, that I found on Microsoft's site, authored by "orangemango" worked for me!! I had tried EVERYTHING up to this point...
go to start search and type cmd search will return cmd.exe right click on this and select 'run as administrator' at the prompt type:- net localgroup Administrators /add networkservice press enter then type: net localgroup Administrators /add localservice press enter then type: exit press enter and restart your computer
I don't pretend to understand exactly why this works, but it fixed my problem!!