The moral of this is always have a backup.
As xeonman13 says nobody can help you without you posting some code. Even if they knew what functions-theme.php is it would be of no help as you say you have been modifying it.
Post the code in the code highlighter tags by using "Go Advanced" and clicking on the icon with php on it.
You could always delete the version of functions-theme.php you have been modifying and start again with the original