This is from a article I wrote for my website about how to get past the white screen of death and it should have enough details for you to get something meaningful displayed about your underlying problem.
If your Joomla website is now a whitepage in the browser with no obvious reason as to why then read on to learn a couple of simple things you can do to point you in the right direction for getting your website back on line.
The most likely reason you are getting an empty white page where your website used to be is that an error has occurred and because you have Error Reporting set to not display(which is the best way to be from a security point of view) in your configuration/global settings then Joomla will display the whitepage with no error message. The tips here will help show you have to change the configuration file manually so the error message is displayed and you will have a better idea what has happened.
First step is to get to your configuration.php via your hosting account so you can change the settings to display the error message that is being suppressed.
If your website is down you can't change the settings via the Global Configuration so you need to have the Userid and Password for the account where your Joomla site is hosted. The most popular hosting service is probably cPanel, while Plesk or Webadmin is pretty common or for some of the bigger hosting companies they may have their own interfaces for managing your website hosting. Once you are logged in to your Hosting account you need to find your way to the File or Directory Manager.
Using the file manager find your way to the root or base directory/folder of your website and look for the file configuration.php and open it for Edit. You may like to take a copy or back up of the file just in case, depending on how lucky you feel.
Scroll through the configuration.php file and look for the following lines with;
public $error_reporting='none', and change that to $public error_reporting='maximum',
public $gzip='1', and change it to public $gzip='0', . This may not be required, but for my hosting accounts error reporting fails when gzip is active.
You may also like to change the public $offline='0', to public $offine='1', to display a meaningful messge, public $offline_message = 'Back soon', while you work on your problem.
Now you can Save the configuration.php file and refresh your website page and the whitepage of death should now have a message describing what line of code has failed. You might be tempted to not change Error Reporting back to None, but that can put your website at risk from malicious activity who may deliberately cause an error to see your account name and file structure
Once your website is up and running you will have access to the Administrator Global Configuration settings you can change the above settings under the first tab and the Server tab.