Deleted code from my pluggable.php doc… my site is now down.

Hello everyone, I really need some help. I just added the feedsmith plugin (feedburner) as a plug in, and when I would add activate, I would get a message that I cannot modify header information. public_html/wp-includes/pluggable.php

After reading the location of the problem, I went to my server and I was messing around with the code, and thought I copied it and pasted it as a back up… but did not and lost all of my code for the pluggable document.

I can’t find new code anywhere, and now my entire site is down with a different message.

Fatal error: Call to undefined function: wp_get_current_user() in /home/nycgr0/public_html/wp-includes/capabilities.php on line 446

I believe it is caused by the missing code from the pluggable doc.

Can anyone please help me?