Lightroom is suddenly not seeing the folders on external drives.

I am a professional photographer and used Lightroom for years and depend on it.

Since yesterday Lightroom seeing only 4 recent folders in a drive which has about 100 folders in the Catalogue 2016

The same is true of other external drives.

Tried reimporting but photos grayed out indicating they are somewhere.

It is not a case of missing folders as nothing has been moved.

Have tried all sorts of things including trying to open backup folder - which I don't really know how to do.

Please help - In real crunch!!

Nan