You need to wait for the mods to answers any PMs. They do have lives like we do and can't be one 24/7.
Also, make sure that you log on the site. Also, you need to check your inbox once in a while. And the tan box (when you log in by using that) can tell you in you got any new PMs. (sometimes a window will pop up, telling you that you got a message)
Example:
You have 0 messages, 1 are unread.