Cause: A white screen is usually generated by an error, which is not visible. IN 99% of the cases most the problem is a limited memory or fatal errors generated by plugins conflict.
a. If you can access the Administration Screens try deactivating all of your Plugins and then reactivating them one by one.
If you are unable to access your Screens, log in to your website via FTP. Locate the folder wp-content/plugins and rename the Plugin folder plugins_old. This will deactivate all of your Plugins.
b. Go to wp-config.php and enable debug to true check errors and take actions based on errors.
c. Rename back the plugin folder and see what errors are displayed. A plugin error will look like fatal error in….. wp-content/plugins/plugin_name/…..
Deactivate or delete that plugin and the website should come back online.
In a un probable case that there is a theme error a the message will look like fatal error in wp-content/themes/wprentals/….. Please note that warnings and notices are not affecting the theme functionality .