Is this an On-Premise or Cloud customer? If On-Premise, we do have a hot fix for a blank window. However, the hot fix also requires a change to a config file so you will need to open a support request so that we can assist with the change. If it is a Cloud customer, then we will also need you to open a support request so we can invesitgate that behavior.
If your settings are held in a local cookie (other than the database) then clearing the local cache should default things back. If they are in the database then we will need to assist. Having said all that, I think a Support Request is the fastest way to a solution.
Senior Director Support Americas