If a white screen showed (with PHP error messages) that means you may have added a PHP error in your code somewhere. This is why I recommend making PHP Code edits using FTP so you have the option to undo any mistakes that are made. You can’t undo PHP code errors using the WordPress Admin, this can ONLY be done through FTP.
Can you let me know what you tried to edit recently? I can help you get it edited the proper way. And if you have an FTP login, that would make it much easier.