In regard to your blank screen, if this is after you have restored the database and have all the scripts in place, then look to the error log and that
may hold a clue.
In regard to upgrading without logging in, you could try restoring the database then uploading all the scripts, then edit the config script to point
to your database etc., then try it and see what happens. Again, the error log may spit out clues of issues. No guarantee this will work, just a
suggestion. The scripts usually have the version number near the top.