Flash Player downloads but Adobe Help says not installed or activated

I have downloaded Flash Player to my laptop which is running Windows 7 and Internet Explorer 11. It seemed to install OK and shows under the Control Panel Programmes list as version 21.0.0.242. Under Manage Add-ons it shows as Shockwave Flash Object  and is definitely Enabled. However if I check the installation via the Flash Player Help page it says Flash Player is not installed or activated. Active X filtering is turned off.

A possibly related factor is that when I go to the Help page I get the error message " An add-on for this website failed to run", but there is no indication of which add-on.

I have had various issues after upgrading from Internet Explorer 10 to 11 so perhaps this problem is something to do with that, eg security settings. One issue is inability to play YouTube videos. The page would apparently open with the rotating roundabout symbol on the black background, but the video would never actually play.

A resolution would be appreciated.