You can restore the index2.php file
See :
http://www.joomlatwork.com/dmdocs/index2.zip
Replace the /administrator/index2.php file.
Note: have you checked if you have the correct file permissions? A blank page mostly indicates file permissions...
Ps. Can I check your site next week (then I'm back with the correct tooling to help you), since this should not happens...
Regards,
Richard