Crashed My Site. Please Help!

Greetings. I recently added a few widgets to my WP site after which I received the following error: “Fatal error: Call to undefined function wp_get_current_user() in /home/content/89/5509089/html/wp-includes/capabilities.php on line 1059”. I looked at the capabilities.php page to see that lines 1058 – 1062 contain the following code: “function current_user_can( $capability ) {
$current_user = wp_get_current_user();

if ( empty( $current_user ) )
return false;

but do not know where the call comes from. I think I know which widget is responsible but I am not able to login to the WP admin panel to deactivate it and I am afraid to delete the widget’s files from the hosting control panel since it has been activated via WP’s.

Can anyone help me to get my site back up?

Thanks in advance.