Question can't access/see posts from other users

I've read several threads discussing similar problems (maybe even related) but I haven't been able to resolve mine so I hope you fine folks have some ideas! I'm far from a master of Joomla or Kunena so I hope I've covered my bases with the info here...

Joomla 1.5.20
Kunena 1.5.11 (then 1.5.12)

Summary:
I can't see replies or new threads started by other test users of my site. Whether I'm logged in as superadmin, moderator, test user or not logged in at all, I can't find the posts. I only know they're supposed to be there because the members tell me and I'm getting e-mail notifications. I can, however, see any posts made by myself under several different user IDs.

Some info:
• The links in the e-mail notifications simply take me to the front page of the forums (the link's URL remains in the address bar even though that's not where I land).
• When logged in as moderator, I see no extra tab for items needing to be moderated.
• I upgraded from 1.5.11 to 1.5.12, no change.
• I uninstalled, deleted all jos_fb tables (via phpMyAdmin), reinstalled 1.5.12, didn't touch config. Problem persists.
• After uninstalling, deleting all jos_fb tables and reinstalling, one of my test users was apparently able to reply to a thread he'd previously started (although it should no longer exist?).
• Doesn't jos_fb_messages contain all threads? If so, I've gotten notifications for two threads that aren't in that table (one that was new post-reinstall, one that was created prior to reinstall).
• Even though one of my test users has posted post-reinstall, he isn't showing up in the user list.
• I've disabled many components/modules/plugins one at a time but haven't found one that makes a difference.
• I've been working on this site for months, Kunena was one of the first components I installed and I have barely had any testing by persons other than myself. However, there was a point where I could access/see the others' posts.

Can this be something as minor as a conflict with some other component/module/plugin or something much more serious?

Thank you in advance!

Addendum:

A brand new test user has just signed up at the site and posted. I can't see his posts and he also doesn't show up in the user list...

Also, I'd asked my test users to post a reply in a specific thread and provided them with a link to it. However, two of my testers have told me they can't find that thread.

I think I've got it -- it's an alternate universe thing, right?

Can these other users see the messages that they've posted?

Yes. In fact, it's as if we're seeing forums on two different websites. One of them sent me a screenshot and they're still seeing (and using) the forums as they were before I reinstalled. And I'm seeing a fresh install and still none of their posts.

I'm guessing I took a bad situation and made it worse somehow...

As a general guide, many of the tips posted in K 1.5.x Support: Please read this first is where I would start. I just have this feeling, in reading the description of your problem, that there's something peculiar in the way you've set up the categories where users post their messages. For this reason I would suggest that you look at Sections, Categories, sub-Categories (Part 2) - advanced setup for special groups .

If other users are able to see their messages when they're logged in to your site, everything now points to what is "special", unusual or peculiar to your login. The key to understanding this is to understand how you've setup your categories. Can you post into the categories that your users can post into, for example?

Have you set "Reviewed = Yes" but you haven't actually approved others' messages, yet?

Could you please provide us with some of the "security settings" that you've applied to your forum.

I don't think it's an installation thing but, maybe, you might re-install K 1.5.12 again just to see if the previous installation was uncompleted or was somehow corrupted?

Sozzled, one thing I forgot to mention earlier is that the complete site was recently moved from the old host (GoDaddy) to the new host (Aspiration) by support at the new host. Also, the site resides on an add-on domain. I don't know if either of those factors could have any bearing on this situation or not...

Also, the way I reinstalled was:
(1) Uninstall Kunena from within Joomla.
(2) Delete ('Drop') all jos_fb tables on that database in phpMyAdmin.
(3) Fresh install.

Did I do that correctly? Just want to make sure before I try it again. (Sorry, I've looked around for instructions but I want to make sure I've understood what I've read.)

In the meantime I'll look more closely at the guide you suggested.

Have you set "Reviewed = Yes" but you haven't actually approved others' messages, yet?

Could you please provide us with some of the "security settings" that you've applied to your forum.

I didn't manually make any adjustments like that -- except for turning off moderation for relevant forums. But (a) I never saw that moderation tab, and (b) this was before I deleted the tables and reinstalled. Since the reinstall I haven't changed any of the default settings.

Thanks for the assistance, much appreciated!

EDIT: Sorry, one more thing. My test users are saying the site is very slow -- the primary reason I changed hosts. I've recently seen a little intermittent slowness but not as slow as they're describing. Could they truly be accessing the copy of the site at the old host?