KOTW was notified that users were unable to post because the Captcha used to prevent spamming was not working.
When posting if there is no Captcha, you should select and copy your post (so you don't lose it) and then press CTRL-F5 (CMD-Shift-R on a Mac) to force a recache of your local browser. The Ctrl-F5 on some computers may require you to press Control-Function Key-F5. Once you have done the above, you should see the Captcha. Complete the Captcha and you will be able to post.