I have got a call from Biomeden. The problem was that he moved to a new hosting but the website was not working. After an investigation I found out that the new hosting has a PHP version of 8.0 so I selected the PHP 7.4 in the cPanel and the website was back on.
Then I got an error when I tried to log in. The wp-admin was led to a 403 error forbidden page.
After investigations, I found out that the wp-admin is a php file which could not execute. I have no idea why it is not working but I found out that if I add the following code to the .htaccess file, it may help to solve the problem
<Files *.php>
allow from all
</Files>