Unable to login to wp-admin and website broken

I went to your website to attempt to see what your issue was but I received a 500 error.

Thanks Bob. What does this mean? How do I go about fixing it?

I have managed to gain access to wp-admin by changing the name of the plugin file in the FTP, however the website still shows a blank white screen with all plugin deactivated

That redirect is correct and expected behavior when you get your site pack up.

Rename what ever theme you are using to themename-old. That will force WP to open with the default theme.