get_the_post_thumbnail() returns nothing?

Try just get_the_post_thumbnail(). Leave the $post->ID out of it.

Edit: Never mind, get_the_post_thumbnail does require the ID. I’d use the get_the_ID() function instead of $post->ID, but that shouldn’t matter.

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