If you have the White Screen of Death, you've got invalid php, or else feel like something fishy is going on, you can display php errors by adding the following line to the top of your.htaccess file. (p.s. make sure your .htaccess is writable/executable, find out how here)
php_flag display_errors on
Important: once you've found out your errors, you should remove this line, as it may breach your security.
Trouble Shooting the WordPress White Screen of Death
6 months ago
[...] every time you make a change, to make sure your php validates. If you've already closed your file, display php errors as shown here, to try and figure out which file is corrupt. Try to [...]