Placed shortcode and received a white screen

Hi!
I tried to get the magic button and failed big time. After pasting the code directly within one of my template files, nothing happened. Therfore I deleted the code again. Obviously that was a mistake or I also chose the wrong file. Anyway ever since my site is gone and I can’t log in no more. Actually by deactivating my theme I got in again, but my site looks like crap right now and I don’t know what to do.
Can anybody help? Thanks.

https://wordpress.org/plugins/ajax-load-more/