Can you please post a url and test user login thanks.
Hard to comment without seeing the site. I will say this though.
To comment you must have the following done
Content visible to verified customers only.
1. You must have in admin option the option to allow commenting set to yes
2. You must set usergroups be allowed to comment set to yes in admin edit usergroups.
3. You must have the groups you wish to comment per category checked off via edit categories in admin as well.