Fix error: Call to undefined function wp_get_current_user()

Hey there,
I’m having some big problems with my website.
I’ve tried installing a new theme, and after that when I go on my website I recieve this error.
Fatal error: Call to undefined function wp_get_current_user() in /home/columb94/public_html/wp-includes/class-wp.php on line 529
I’ve tried fixing it by disabling the theme, disabling all the plugins, reinstalling the wordpress, the reinstall is working but when I go into wp-admin it fails again.

The website is: http://www.columbofil.com