We're sorry to hear that you could not use Cornerstone fully. There are many possible factors that could cause that though. I'll list the potential ones based on what I currently see on your site and screenshot.
1. You're using optimization plugins namely Autoptimize and W3 Total Cache. To quickly test if they're causing the issue, please clear all caches of those plugins and temporarily deactivate them.
If the issue's fixed, one of them is certainly causing the issue. In this case, you'll need to contact the developers or support of those plugins to teach you how to exclude the backend from being optimized and cached.
If the issue's not fixed, please don't activate your optimization plugins yet and proceed with further troubleshooting. Steps listed below.
Please just note that we're not against optimization. In fact, we have a Performance Guide here: https://theme.co/apex/forum/t/customizations-performance/210
The important thing to realize though is that optimization plugins are configured or should be configured depending on the overall setup of your WordPress site and our themes and plugins are just parts of your site. With that said, our guide might not work for your particular setup and we do not cover website optimization as part of our product support.
2. Another plugin could be causing the issue so try testing for a plugin conflict. You can do this by deactivating all third party plugins, and seeing if the problem remains. If it's fixed, you'll know a plugin caused the problem, and you can narrow down which one by reactivating them one at a time.
3. You're using a child theme and if you've added custom codes in functions.php or in other templates and the code is outdated or contains errors, it could cause issues. You can quickly test if the issue is coming from the child theme by activating the parent theme. If it's fixed, please hire a web developer to fix the custom codes. Please note that my statement includes custom codes found here in the forum. They're only meant to provide customization guidance and not part of our product's functionality.
Only if you have tested the factors above and none of them is the cause, please give us the following details in a Secure Note
- WordPress Login URL
- Admin Username and Password
- FTP Access