cannot login in admin

I just had my ISP upgrade me to 2.5. When I go to the admin screen and try to login, I get this error in my browser (firefox, does same thing in IE);

Fatal error: Call to undefined function: wp_register_sidebar_widget() in /home/wmumford/public_html/willfishforwork/wp-admin/includes/dashboard.php on line 31

I’m not much on code but can muddle through basic stuff, ok making changes with decent direction- thanks!