If you see a blank page, or start an operation that appears to never complete, or receive a 500 error code, it’s likely that you have encountered a PHP error. In order to find out the cause, you’ll need to check your PHP error log for details.
Where you’ll find your PHP error log will depend on your server’s setup. In most shared hosts, there is a directory called logs or something similar. If your server uses CPanel, you may have an entry there called “Errors”. You may also be able to check your phpinfo() page (example instructions).
If you’re running your own server, logs will usually be somewhere like /var/log or /var/log/apache. They might be combined with the Apache log, or in a separate file, again depending on the server’s configuration.
There are many useful threads in StackOverflow that may help to find your logs (example).
Unfortunately it is difficult for us to give specific instructions, as the details will depend on your server’s configuration. Normally a service provider will have a knowledge base, which should contain detailed instructions.