Hi Vertex,
Thank you for the credentials, the /wp-admin login works but not the FTP, it seems to be pointing to an empty directory. Please check so we can take a closer look.
Anyways I investigated the issue, and there seems to be an issue with W3 Total Cache, I would suggest uninstalling the W3 Total Cache at this point, please follow the instruction provided here.
Also, the Wordpress is giving notice that your .htaccess is not writable, so you need to put that mod_rewrite rules manually on your .htaccess via FTP. You can see this notice and the mod_rewrite rules under Settings > Permalinks.
It is important to resolve that W3 Total Cache issue first because it seems all the errors on your site are related to caching.
Let us know how it goes,
Cheers!