Fatal error that won't allow me to login to my wordpress.org site dashboard

I have a wordpress.org site: http://www.sufijournal.org/wordpress.

On Sunday I tried to reinstall a twitter widget (I think it was WP Twit Widget but not 100% sure) that I thought I had deleted but it turned out I hadn’t and it immediately gave me this fatal error:

Fatal error: Cannot redeclare widget_twitter() (previously declared in /home/content/41/6631241/html/wordpress/wp-content/plugins/wp-twitter-sidebar-widge/twitter_wid.php:132) in /home/content/41/6631241/html/wordpress/wp-content/themes/magazine-premium/widgets/widget_twitter.php on line 41

Now my site won’t load at all (just produced a white screen with the fatal error text) and I can’t login with the login details I usually use for that wordpress.org site anymore – wordpress doesn’t recognise my login details – so I can’t access the dashboard to delete the conflicting widgets.

I would be really grateful of any advice/assistance and can provide more details if needed.

Thanks!