The problem is that recent versions of PHP have dropped suport for coding used in vBulletin. You can check out what the old version of vBulletin returns here.
The oldest version of PHP available and the one currently installed is PHP 5.3.29. This version is not officially supported and even support for 5.6 is expected to end in a few days. Using the instructions for changing the version of PHP here do not seem to work on this server. So, having the oldest version installed on non-working instructions, there are dim prospects this can be readily solved by changing PHP version.
While vBulletin is no longer available, the SQL database containing the postings appears intact. All of the postings made to vBulletin are available for download here and auxiliary tables here. Navigation is missing and the dates are in internal format but if it is really necessary to access this data, you can download from this page.
Alternatively, you can log into cPanel, click phpMyAdmin under Databases, expand admin, and click admin_forum. The complete vBulletin tables are listed with the vb3_ prefix.