Urgent, need help.

I asked some help, and your staff advise a code    See this issue link.   

As soon as i saved those code, my site is dead.  even my wordpress can not open. 

Say: http error 500.    what can i do?        Besides: my function.php already has other code before i add these code, but i can not login, i can not show you. 

Thanks for your quick reply