It looks like you added the wrong code to your functions file. Assuming you have the latest version of Genesis 2.0+, if you add the older code (for anything before Genesis 2.0) it can cause php conflicts. Especially if there is a PHP error. When your site shows up like that, it’s usually a PHP error or typo.
There are 2 things you can do –
1. Login through FTP. Locate the functions.php file that you edited and remove that code, or replace the entire file with the default functions file.
2. Contact your host to see if they can load a saved backup of your site, so you can log back in.
In the future, I always recommend that everyone use FTP when editing files. Especially PHP files. The reason is, if you edit a PHP file in WordPress and make an error or a typo, your entire site will go down (as you can see) and you won’t be able to go backwards to fix it since the PHP error breaks your entire site.
If you have Genesis 2.0+ (you should) the code from the link you posted won’t work since it is for the XHTML version of Genesis. There is no Return to Top in Genesis 2.0 (they removed it). Genesis 2.0 has separate code for the new HTML5 version. Make sure you add the correct code (HTML5 version) to your functions file when making edits.