Thanks. I followed the purge and reinstall procedure, but the problem with the blank entry when viewing Control Panel from Start10 is exactly the same as before, and as before the blank entry is not visible when viewing Control Panel from Windows Explorer.
p.s. If I configure Start 10 to display Control Panel as a link instead of a menu, then the blank entry isn't there and the NVIDIA entry is in correct alphabetical order. The problem only happens when I choose to display Control Panel as a menu.