If your website displays only a white page without any information this usually means that a script error is present.
You can review what caused the error (in most cases) by consulting your Error Log in your control panel:
Visit the 'Domains & Hosting' tab and select your domain on the left hand side (don't tick the box). Next to 'Your website', click on the cog wheel followed by 'Error Log'.
You can review the error messages on your site here (if any). The description can be a bit technical but problems usually point to a specific line in a file. Most errors have one of three causes:
The solution for this is to simply rename or remove the corresponding folder that contains the plugin or theme. You can then reinstall the plugin or theme to solve the issue. In these cases you can use the sFTP file manager in your control panel.
From here, head to the 'Domains & Hosting' tab at the top of the page and select your domain name on the left hand side (don't check the box).
Next to 'Your website', click on the cog wheel, followed by 'SFTP filemanagement'.
Navigate to the 'www' > 'wp-content' > 'plugins' or 'themes' folder and search for the plugin or theme that is causing trouble. Rename or remove the plugin and you will be able to log in to your WordPress Dashbaord once more. Now reinstall the plugin / theme or search for an alternative plugin / theme to use.