nothing shows on the screen..
Do you mean you have an entirely blank screen or just that the image doesn't display? Does View Source for the page reveal anything?
Please edit your code: the closing tag is [/ CODE] (without the space) and there is a separate button for PHP code-wrapping.
$fontname = getenv('GDFONTPATH') . '\comic.ttf';
You might need to double-escape \\ these, and access to this C-drive location may be an issue (even if just testing it locally). Added
: I think you might need to save a font (.ttf) within your domain(?).