Hello and welcome to Just Answer! I am Aitizaz and i will help you today.
Did you install anything on your website after which this has happened?
OK! Please DEACTIVATE all plugins on your website,then try to open the website. If the website opens fine, ACTIVATE the plugins one by one and check your website after you activaye each. Let me know the result then
You should have disabled the plugins through admin panel earlier. However in the given situation, we need to rebuild the .htaccess file. How much time do we have for this?i will not be able to work on this for 8-10 hours from now
In case this is urgent and you cannot wait,i will refer you to any other expert. Do you want me to do so?
Sure, thank you for your patience