How do I set up my blog home page to show only this weeke’s posts automatically?

According to docs you can retrieve such set of posts by using Time Parameters with query_posts(), but note that it will likely horribly break your pagination and links to older entries.

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