Now i am blocked out of the supper admin area in my web site

I am at a lost for my site http://www.nuwshop.com i am now blocked out of my super-admin area all the sites are working fine from what i can tell but i get this string of code "Call to undefined function wp_get_current_user() in /home/ninedrop/public_html/nuwshop.com/wp-includes/capabilities.php on line 1281" earlier today the images started not showing up and now i am blocked out of the admin area. When i talk to host Gator all they said is " It just appears to be an issue with cache and scripting." not sure what to do at this point.

Thanks in advance