I got the blank screen as well. As I don't follow instructions well, I ended up having to go through the new database (1.3.8) and visually compare it to the old database (1.3.7). I opened a backup SQL of 1.3.7 database and compared it to the 1.3.8 database in the zc_install/sql/mysql_zencart.sql.
I used the 'Install SQL Patches' and the 'PHPMyAdmin' on my server to go through every table manually. Made sure that all the table prefixes were named correctly, then would insert the old data into the new (1.3.8) tables.
This method took some time, and trial and error, but I highly recommend it in order to get to know about what is going on behind the scenes in your database.
One must be very thorough and check/double check that everything looks correct.
After getting some errors in the admin area, I had to change a few lines of code in admin/includes/fuctions/general.php to match up with the database tables.
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