500 internal server error site missing

Entire site appears to be gone after the error occurred. Logged in and no pages are found. An error occurred when updating My Custom Functions Plugin, was adding code from support site to require the last name on the donation form, was missing a few lines of the code. Tried to replace the code and error continued. Tried to access Wp Admin and error occurred. Tried to access the site via internet error occurred. Tried to view a site page in WP, received index error. Logged out and logged back in and site appears to be empty. OMG HELP!!!

The page I need help with: [log in to see the link]