Hi everyone and thanks for your kind help.
I was cleaning a friend's site that is constantly attacked by malware and my hosting had a guide about how to do this from scratch. Basically I've:
Cleaned everything with Wordfence.
Downloaded the last version of WordPress.
Deleted everything except "wp-config" and "wp-content". Then deleted the plugins and themes.
Reupload all the clean WordPress files that I downloaded before.
Now nothing works, I get a 500 error and my hosting assistant told me that "a file is lacking (version.php) in the installation. The file wp-setting.php is calling line 33 of its code and cannot find it".
I've already tried to reupload the clean files and it's still the same. I cannot reconnect with the web.
The web is https://escuelaxlski.com/ and was designed in Oxygen.
Thanks so much.