Make sure you're actually going to /core/install/install.php rather than just refreshing the page. As refreshing the page will simply reload makeconfig.php. You need to start from scratch at /core/install/install.php. As long as you have both config files renamed and the core config file populated with valid database credentials you should get straight to the install process.
If you need to raise a ticket go here:
http://www.vbulletin.com/go/techsupport
You'll need to request that the ticket is sent to me.