Can't see 'Upgrade Database' anywhere

I'm upgrading from 1.3.9h and I'm happy to loose customisations as the site needs an overhaul but I do want to loose the database.

-I created a new database in cPanel.
-Exported old database and imported into new database with phpMyadmin.

• Created a new folder on server and uploaded zecart 1.5.0
• ran zc_install and put in details for the new database, using same database username and password as old site.
• went through the rest of the installation process.
• opened admin section on new site.
• database is empty.

I checked the database and it's an exact copy of the old one.
I checked the config.php files and the database prefix (none) and database username and password are identical between the new and old sites. Only difference is the database name.

The instructions say 'choose upgrade database' but I'm never given the option.

What gives?

The "Database Upgrade" option only appears when the system is able to use the DB_XXXXXXX settings in your /includes/configure.php to connect to a database and finds valid prior-version Zen Cart tables in that database.

If the button isn't appearing, then ... it's not finding Zen Cart tables/data in the database specified. So the database name/host/password/prefix is wrong.

Before I was creating a new database with the same database username and password, exporting old one and importing into new one. When I chose the new database, which is exact copy of old one, the installer never shows update button.

This time I exported the old database for backup and used the exact same database name, username and password for the new install and still, the installer finds nothing. I even brought up the configure.php from the old install and copied and pasted database name, username and password to make sure I made no typo's.

I checked with phpmyadmin prior to install and database is as it should be and old install works without a hitch. After new install my database tables are all cleared (lucky I backed up!)

Why is this happening?

Re-import the 1.3.x data into the 1.5.0 database, and make sure the configure.php files in the 1.5.0 area have the correct DB_PREFIX to match what your 1.3.x DB_PREFIX is.
Then run zc_install, and it should give you the upgrade option.
If not, what's the URL to your zc_install on the 1.5.0 test area?