My b2evolution Version: 2.x

I have 't do anything recently. haven't upgrade or changing password.

I just suddenly find that when i go to my blog. it was strange and i can't login anymore. what can i do?
http://www.lovenature2007.com/1a.jpg

i have tried to find the answer like: changing the _advanced.php file

which read:
$instance_name = 'b2evo'; to 'qwerty';.

but it wasn't work.

And i have also go to phpMyAdmin to change the password, still can't not login.

And i tried to submit as a new member, but new member also can't login!!

Anyone can help me?