What Web browser are you using? It seems that a lot of Internet Explorer 9 users are unable to get the New Posts function here on the forums to work. I am still at I. E. 8, having disabled the Internet Explorer 9 update from installing through Windows Update, and the New Posts function seems to work fine for me. If you are using I. E. 9, then perhaps reverting to Internet Explorer 8 (if that is even possible) or switching to Firefox would be the answer.
Regards.