Don't panic yet ...
I am pretty sure you just damaged a tpl_ file or a language file ...
What you can do is download the Debug Tool from the Free Software Add Ons ... and look to see what errors show up ...
That is going to generate files with errors listed in it ... be sure that when you try to see the files in your FTP program that you refresh the display as they will not show until you do ...
More than likely it is just a moofed up piece of code or a space(s) or blank line(s) at the end of a file that is making you "look" all destroyed ...