@Amfisse, seemed like most of the core files are missing. The problem might be you accidentally deleted or something wrong with the file transfer.
My suggestion is if you have contract with web development for your site, notify them as soon as you can.
or If you build your self, backup the theme folder, plugin folder(main plugin folder) and database. Install the fresh Wordpress and copy and pasted the backup file to the same directories.
If you happened to change the site url for fresh install, change the url of wp_options table (wp_ might be depend on the prefix you choosed) where column name is 'siteurl' and 'home'.
I hope this advice would help you. Good luck with your fresh install :)