3.8.7 login action page is blank, cannot proceed

[RS25.com]

I am running VB 3.8.7 - when trying to login, users and I get to this URL:

forums/login.php?do=login

which is a blank page and returns a 500 internal server error. My server is not giving any useful information on what is happening. However, if you manually go to the home page, you are now logged in.

The problem is that I cannot login to the admin. The page goes blank, but the admin does not recognize me as being logged in.

I have done a side-by-side verification of my PHP code to the vbulletin code which I downloaded from the members area. Everything is identical EXCEPT the /forums/includes/md5_sums_vbulletin.php file. However, the date inside the file is also different, so I suspect that is okay - right?

Does anyone have an idea why this is acting like this? Only a few days ago everything was working.

I have a helpdesk ticket in with my host, but I am not sure what they can do to help.

[Mark.B]

Please try the following:

To disable the plugin/hook system completely, edit includes/config.php and add the following code:
Just below

<?php

enter

define('DISABLE_HOOKS', true);

Does this fix the issue?