ISSUE: Theme install worked, but when Customizer loads, it looks broken.
Typically, if you are loading the Customizer under Appearance > Customize and it doesn't look right (i.e., stripped of formatting, no tabs related to your new theme, etc.), it is due to a plugin you are running. Often, these plugins are from an old theme you were using, and need to be deactivated. You can delete the plugins altogether if you have no plans to use your old theme again.
As a first line of troubleshooting when the Customizer won't load or just doesn't look right, be sure to audit your Plugins and deactivate any that are associated with an old theme. And while you're at it, deactivate (and delete!) any you know for sure you're not using anymore.
Below is more specific guidance for issues with the Customizer, based on previous themes you may have been using, as well as additional troubleshooting options.
Genesis Framework Themes
If your old theme ran on the Genesis framework, be sure to go to the Plugins page from your WordPress dashboard, and ensure any plugins relating to Genesis are deactivated. For example, many customers who were running the Genesis Feature Page Advanced plugin will find it breaks the WordPress Customizer (the issue will look like this):
Our themes are not built on the Genesis framework, so any and all plugins relating to Genesis should be deactivated.
If you were previously running a Pipdig theme, please be sure you have deactivated the Power Pack Plugin. The Pipdig plugin adds a lot of functionality that can conflict with other themes.
Corrupted .zip files
If you're installing your EmPress theme on a fresh site (i.e., no theme existed before your new one), and you're still having issues with the Customizer, it's possible there was an issue with your .zip file. This can happen if you downloaded your theme .zip file in Safari, and then manually re-zipped your theme file.
If this sounds like it could be the cause, please try downloading your theme .zip file in a different browser. You can download a fresh version of the .zip file by accessing your account at empressthemes.com/account. Check out this Help Desk article for information on where to access previous purchases.
Critical Error Message
Occasionally, following successful theme install and activation, some customers may see a critical error message when they try to load the theme Customizer. This may also occur if trying to load the Customizer without activating the theme, to view a theme preview.
Please read our Help Desk article here for how to resolve this issue. It often requires a more thorough plugins audit!