If you do something and get a blank white screen in your installation, this means it is a php error. the message is suppressed for security purposes.
If you were editing a file, revert your last change.
If you installed & activated a new plugin, remove the plugin.
If you upgraded a plugin, check and see if it's compatible with your version of WordPress.
If you upgraded, turn off the plugins by renaming the plugins folder to something like plugins-old. Do the same for the mu-plugins folder.
Your server may write an error log to the server somewhere. Ask your webhost where they are and read them. They will often specifically state what file was the problem, and what line number too.
