Update Button Unavailable in Page editor

Logged-in to make modifications to certain pages and in the publish option box there is no option to update the page.

The only button available is the Preview button.

I had made modifications to the WP-Includes folder modifying the button-min.css, and the editor-min.css files.

Only new plugin that was added was system snapshot.

I’ve tried changing the plugin folder name to temporarily disable all plug-ins, and this had no effect. I’ve also reverted back to my backups for the files I edited, and still had no luck. I then downloaded a fresh install of WP and reinstalled just the WP-includes folder, but save draft is still unavailable.

Help ??