Error 404 when trying to edit anything

Hi, the site was all good until today when I try to edit any page or post or anything, I get a 404 error. I checked for permalinks also but it didn’t work. I found two files named “.htaccess” and “.htaccess.old” in the folder. I pasted the following code in the “.htaccess” file and then got a 403 Forbidden error.

# 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

Your help will be highly appreciated.

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