Upgrade from 1.5.1 to 1.6.4 not working

I am on a Windows server trying to upgrade from 1.5.1 to 1.6.4 and cannot get it to work. I have tried the following

1) Copy the C:\xampp\htdocs\Xibo\settings.php to desktop for backup
2) Extracted the 1.6.4 files to a folder
3) Renamed C:\xampp\htdocs\Xibo to C:\xampp\htdocs\Xibo_original
4) Created a new C:\xampp\htdocs\Xibo folder
5) Copied the contents of the 1.6.4 folder into the new Xibo folder
6) Opened a browser and went to http://servername/xibo (also tried http://servername/xibo/install.php) and all I get is a blank white screen. It never goes any further or gives me any errors.

Please help.

thanks,

Paul