Avatars's broken my website, what to do?

I started to install plugins from wpmudev dashboard and after activating Avatars fatal error occured:

Fatal error: Class 'WA_Widget_Avatars' not found in /home/clisauto/public_html/clispress.uk/wp-includes/widgets.php on line 413

. None of pages on clispress.uk works, what can I do?