If this is a new install. or just moved or just upgraded or some of the above?
What version are you on?
First Item I would check is file permissions.
You could start in cp-tools&information -permission checks.
and or follow the installation guide.
Next is the group/forum/site permissions..
start with Can approve moderated posts.
There are a lot of permissions to deal with..
So it is vvery easy to overlook something in error.
Posting the url to your site may help.
If one of us has time we can register and post to test.