Manually disabling Wordpress plugins: Occasionally plugins can have issues that will cause a site to become unreachable, normally displaying a "There has been a critical error on your website. Please check your site admin inbox for instructions." message.
To bring your site back online, you will need to do two things. The first is enabling Wordpress Debug messages. The link below will walk you through how to do that.
Once you have enabled debugging, navigate back to the folder containing your Wordpress install. From there, you should see a folder named "wp-content", and inside that folder will be another folder called "plugins". Find the plugin that is causing your site to fail, and right click on it. Select "Rename" from the options and add ".disable" to the end of the plugin name. This will disable the plugin and in most cases bring the site back online.