I can see that some of the YUI library files are failing to load for your home page, for example:
Request: GET theme/yui_combo.php?rollup/3.17.2/yui-moodlesimple-min.css
Response: 404 Not found
Request: GET theme/yui_combo.php?rollup/3.17.2/yui-moodlesimple-min.js
Response: 404 Not found
Have you performed the URL rewriting or Optional UTF-8 file name fix steps from the IIS page in the docs? The documentation is a little confusing but it looks like either one change or the other is required. But it does mention that YUI files may not load correctly without these changes.