When submitting the form site.com/blog/wp-admin it goes to site.com/wp-admin

You have to define the home url, in the installation folder of site.com/blog:

define( 'WP_HOME',' http://site.com/blog' );
define( 'WP_SITEURL', 'http://site.com/blog' );

I think this can solve your problem.

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)