Looking at your site, it is not even opening static files like the readme.html or the license.txt so I believe it may be more an issue at the server-end rather than the WP core code.
Could you check if that can be fixed? And then we can try to figure what’s not working with the actual WordPress installation.
If you remember and know which version of WordPress you were running on, you could do the following,
1. Download the WordPress zip from the releases list,
2. Unzip it on your local system/computer
3. Back up the files and folders on the server. Also the database.
3. Finally replace all the files and folders (except the wp-content folder) like index.php, wp-login.php wp-includes & wp-admin folders etc.
Note: Please keep a backup of the wp-config.php file, the wp-content folder, and the database as if they are lost, it will be very difficult to get the site back to the older version without putting a lot of efforts.