Unable to open my website and can't login to wp-admin

It appears you do not have wordpress installed yet. https://codex.www.ads-software.com/Installing_WordPress
This should help

Is this a new install of WordPress?

It isn’t a new install of WordPress. I visited the web site two days ago and it worked but not today. It is not directly my site but I have to make some modify for a client and he told me he didn’t do anything changes

Right now, I am seeing:

The page isn’t redirecting properly

Firefox has detected that the server is redirecting the request for this address in a way that will never complete.

Try:
– switching to the default theme by renaming your current theme’s folder inside wp-content/themes and adding “-old” to the end of the folder name using FTP or whatever file management application your host provides.

– resetting the plugins folder by FTP or phpMyAdmin.

oh, I’m trying to reset by ftp but when I try to log in https://www.gretamastroianni.com/wp-admin/ I am not able because it shows me the same error page

You do not need to login to your WP site to use FTP. If you haven’t used FTP before, ask your hosts for assistance.

I am able to log in the ftp but I am not able to log in my WordPress administration menus (/wp-admin) (I’m following the procedures, poit 3 https://codex.www.ads-software.com/FAQ_Troubleshooting#How_to_deactivate_all_plugins_when_not_able_to_access_the_administrative_menus.3F)

I paste here the four poinnts of procedure:

Or reset your plugins folder via FTP or the file manager provided in your host’s control panel.

1. Via FTP or your host’s file manager, navigate to the wp-contents folder (directory)
2. Via FTP or your host’s file manager, rename the folder “plugins” to “plugins.hold”
3. Login to your WordPress administration menus (/wp-admin)
4. Via FTP or your host’s file manager, rename “plugins.hold” back to “plugins”

Have you renamed the plugins folder yet and/or your current theme’s folder?

Yes I have just renamed both the themes and plugins folder

Um – what exactly did you do? Which theme folder did you rename?

I renamed th themes foldere in –> themes-old and the plugins folder in –> plugins.hold

No. That’s not what I suggested. Change the wp-content/themes folder back to just themes. Then try switching to the default theme by renaming your current theme’s folder inside wp-content/themes and adding “-old” to the end of the folder name.

Oh sorry, I didn’t understand well. Inside my Themes folder there are two folders and a file called index.php. I add the ending “-old” to both of the two folders, is right?

No! What is the name of the theme that you are currently using and what are the name of the two folders inside wp-content/themes?