If Zen Cart cannot read the configure.php file or finds default settings in it, or finds invalid data in it (ie: cannot connect to database using the settings therein), then it assumes that it hasn't been installed and attempts to load the installer.

Check that your 2 configure.php files are readable and that they contain correct information for URLs, file paths (DIR_FS_CATALOG, etc, DIR_FS_SQL_CACHE, etc).

This FAQ may be useful:
https://www.zen-cart.com/tutorials/i...hp?article=100
this one has similar info:
https://www.zen-cart.com/tutorials/index.php?article=99
and this one is related, in case you're just moving to another folder on same server:
https://www.zen-cart.com/tutorials/i...hp?article=122