Page Not Found Error-404 when accessing WP-Admin

When I log in to the Dashboard for my WP-Admin, I can usually see the Dashboard itself, sometimes I can click on one more top-level menu item, but any other clicks on the screen lead to a Page Not Found error-404.

Does anyone have a way to get in to the Admin area? I can’t even troubleshoot without access.

My problem is similar to this: https://wordpress.org/support/topic/trying-to-update-pluginsthemes-or-settings-redirects-to-page-not-found?replies=13, except that I haven’t even gotten to 4.3 yet.