Password keeps chaning

Hi there.

I have a serious problem with my wordpress site. It seems that no matter what I do I can’t change the admin password in phpMyAdmin. I change it and it looks ok but when I try to login to my wp-admin section it says that the password is incorrect. When I go back to wp_users table in database I see that password has been changed back to its first state. Do you know any solution to this problem. I think I have been hacked!
I can’t access my admin area to change the content of my blog.
It all started yesterday when I loged out after automatic upgrade from 3.0 to 3.0.1.

Please help.

Regards,
Leon