The error that your site presents is due to a redirect loop. Before you move anything into files on your site or database, try the following:
If you have lost the .htaccess generate it again:
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress
If you use SSL, your .htaccess should look something like this:
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{ENV:HTTPS} !=on
RewriteRule ^.*$ https://%{SERVER_NAME}%{REQUEST_URI} [R,L]
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress
Delete your cookies (those of your site) and try ...
See if you have the same problem. If so, and to find out what is causing it and try to solve the problem, try entering your FTP and disable the plugins (change the name of the folder for any other, later restore it). If the error disappears when you disable the plugins, it now restores the name of the folder and tries to perform the same procedure with each of the plugins to determine which or which are causing the problem.
Remember to erase cookies and temporary files in each attempt. I hope it serves you.