Single Posts Not Showing At All… Help?

if the site works except when you go to single posts, your changes are probably to blame.
Did you check the error log to see if a php fatal error has happened?

I would do a backup, then get a fresh copy of the theme and copy the single.php into the theme folder using FTP or use the theme editor and replace teh existing code in the current edited single.php with the virgin copy.

closing as duplicate