The blank page is generally caused when the database server cannot be reached by Confluence or the database service is not started.
In case the database is located on a different server, I suggest you ping this server from the Confluence server and make sure there's no network traffic issue.
In addition, you can verify the atlassian-confluence.log file from the Home-Directory/logs folder to have a better understanding of what is happening.
I believe you're having as issue similar to the one mentioned here: https://confluence.atlassian.com/display/CONFKB/Unable+to+start+due+to+net.sf.hibernate.exception.GenericJDBCException+Cannot+open+connection
These are the main investigation paths we can follow initially. Otherwise, I suggest you raise a support ticket at support.atlassian.com.
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