Is it a good idea to rename the “index.php” in “wp-admin” folder to avoid being hacked?

Renaming files will not make your blog more secure. Obscurity, hiding trivial information, is not a real security concept.

The index.php is safe. Make sure the file permissions are set correctly, and try to find the real security hole you had.

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