Will explain what caused problem!
When we installed vb 3.8.11 - we got message that we must delete install directory for access to admin cp
when uploaded your files - install directory missing some vbulletin files - i copied vbulletin files and could run upgrade.php - otherwise was just blank screen!
glad you figured it out, yes that's basic vBulletin procedure when upgrading / installing you must always have the install folder. Instead of deleting the folder from your server for future need, it is better practice to rename it something random. like .34hp98hregf798dhpg9