Which editor interface were you using before? Has that setting changed for you? On the Edit Options page (which you can reach through this link or through the My Profile or Quick Links buttons above) there's a box describing the choices:

Message Editor Interface
When posting messages to the forums or other members, there are three interface types available to you. The simplest of these is a simple text box, while the last is a fully-fledged WYSIWYG editor, which allows you to format your text as you want it and see the results immediately.

Depending upon the capabilities of your web browser, you may not be able to use all of these options. If you experience problems when posting messages, try switching to a different interface type.

Try all three and see if any give you better access to the smilies.

Also (though I think this only applies when you reply, not when you start a new thread): the Quick Reply box offers you a smaller set of smilies than the Go Advanced box but either one provides a link ("More") to the full set.

If you're seeing an editor interface that you recognize as the one you've been using and only the smilies are failing to appear, that's a technical glitch (somewhere, maybe at this end, maybe at yours). I'm currently using "Standard editor, extra formatting controls". I started out in "Quick Reply" but I've clicked "Go Advanced" since then, and I'm seeing the usual set of smilies over at the right.