Thumbnails Intermittant to display and stuck on Large view
 

This is a recent problem, which is driving me nuts.
In W10.
When I open up my Pc etc. to display what is connected, it takes forever and when it fires up with the content it again takes forever to open up a file.
e.g. an external HD with lots of photo files.

It is then very slow to show the files., Mostly I eventually get blank or missing thumbnails.
When the thumbnails eventually come to life they are stuck on "Large View" , with other view options greyed out.
Before this problem all PC actions and files were working at speed and no problems.

HELP!!!!

With thanks for any ideas as to what may be the problem.

On line actions, e-mails etc. all work fine at a good speed

OPF