Can you output the contents of your config.php file (without password salt, ID, passwords, etc)? It’ll look something like this blanked out:
Additionally if you use Chrome, Firefox or another browser with page inspection, right click on the broken page, click inspect element and look out for the errors:
This will potentially give an indication of the path your install is trying to load scripts from.
It sounds to me like it’s been installed to be accessed via internal IP and the overwrite.url is the local IP rather than a FQDN.