So is this a new installation?
Have you checked the server requirements
xot.xerte.org.uk/play.php?template_id=81#systemrequirements
including the required extensions?
Was everything confirmed as ok during setup?
What have you setup as the authentication method - is the account you're testing with a DB account? If so does the sup folder in USER_FILES contain the correct username as part of the folder name?
Anything relevant in the apache error logs? Set development=true in config.php and then check the apache error logs as well as the xerte debug.log.
Anything relevant in the browser console when you get the empty window?
Sorry all questions and no answers but those are the things to check and test.
HTH
Ron