Preview Changes not working

Can you access the Users section of your Dashboard? Does it say your user level is Administrator there?

MacManX – Yes, it does.

Ok, try downloading WordPress again and delete then replace your copies of everything except the wp-config.php file and the /wp-content/ directory with fresh copies from the download. This will effectively replace all of your core files without damaging your content and settings. Some uploaders tend to be unreliable when overwriting files, so don’t forget to delete the original files before replacing them.

If that doesn’t resolve the issue, try deactivating all plugins. If that resolves the issue, reactivate each one individually until you find the cause.

If neither of those resolve the issue, try switching to the Twenty Fourteen theme to rule-out a theme-specific issue (theme functions can interfere like plugins).

Ok. Installing WP again didn’t solve it. But I did find 2 plugins, Captcha and WP HTTPS, that weren’t working with the new version of iThemes Security (iT Sec).

After reseting iT Sec, I fixed the problem by unchecking Force SSL Exclusively box within the WordPress HTTPS settings. It solved multiple issues.

Excellent, thanks for sharing!