Loss of Widget Functionality

Help. Recently A lot of spam has been getting through.And now I have discovered that it is because the entire widget section of my site has ceased to function! Unfortunately before I discovered that I tried to install a ‘Change your Username’ widget, as a warning in red said that to use ‘admin’ as my user name was dangerous. However, I must have done something wrong when trying to install this and now it appears to have taken over my complete site and a load of writing is superimposed on my page. But much worse than that, nobody can log in- INCLUDING ME! I can’t access my admin page so there is nothing I can do about my problem. I seem to be requiring some sort of remote help. I have no idea why or when my entire widget section lost it’s functionality but that is the root cause of my problem. I think that my version is 3.3.1 but I can’t get in to check. I will include below the email I got alerting me to various problems, I don’t even know what ‘your DNS records have changed’ means let alone how to fix it!

Wordfence found the following new issues on “Cymdeithas Rhandiroedd Maesgeirchen & Tan y Bryn Allotments Association”.

Critical Problems:

* WordPress core file modified: wp-content/index.php
* The Plugin “Author Avatars List” needs an upgrade.
* The Plugin “Jetpack by WordPress.com” needs an upgrade.
* The Plugin “Login Logo” needs an upgrade.
* The Plugin “Uber Login Logo” needs an upgrade.
* The Plugin “Wordfence Security” needs an upgrade.
* The Plugin “WP-PostViews Plus” needs an upgrade.
* The Plugin “WP Google Fonts” needs an upgrade.

Warnings:

* Your DNS records have changed

Please do what you can to help.
The site is: http://www.allotmentsmaesg.co.uk/