I have successfully been using WP to build my website until a week or so ago.
Recently I installed the CLEF WPplugin (single password tool) which was working OK before I went away.
After returning from a 3 week trip I find that the WP Admin Dashboard features which allow editing/adding pages/blogs, list & all plugins etc are missing and the CLEF password plugin had stopped working.
Only WP features available are Activity and WP News under the Dashboard Tab - No listing for Plugins, Pages, Themes etc.
I have gone to my PC Panel and deleted the wp-content/plugins/wpclef folder which allows me to log into my WP site but still unable to edit my site content.
When I open my website in browser everything is visible, I just can't edit it.
Any help would be gratefully received.
Not sure if this is the answer to your problem or not, but Clef is shutting down next week: https://www.wordfence.com/blog/2017/03/clef-shutting-down/. So, even if it isn't the cause of your current issue, you need to get rid of it ASAP.
You may need to access the WordPress database via PHPMyAdmin to check your User Account to make sure you still have the Administrator role.