Thanks for writing in.
If you download the Pro theme its already zipped version, no need to zip it again. That's why it's showing you missing a style.css file.
Please remove the Pro folder completely and reinstall it. After that install Pro, and disable the cornerstone in Dashboard-> Plugins.
Please check install guide for help.
In case the issue persists, would you mind providing us with login credentials so we can take a closer look? Please provide following information:
Set it as Secure Note
* Link to your site
* WordPress Admin username / password
* FTP credentials
All the best!